Facile synthesis of iron oxide nanoparticle and synergistic effect of iron nanoparticle in the presence of sunlight for the degradation of DOM from textile wastewater

Facile synthesis of iron oxide nanoparticle and synergistic effect of iron nanoparticle in the... This study explores the capacity of synthesized F e O nanoparticles (NPs) under sunlight for the degradation of dissolved 2 3 organic matter (DOM) from synthetic (Procion blue dye) solution as well as from textile wastewater (TWW). Fe O NPs were 2 3 properly synthesized and confirmed by UV absorbance, FTIR spectra and SEM image analysis. Photocatalytic degradation of DOM from TWW and synthetic solution was performed by catalyst F e O NPs (5 mg/L) in the presence of solar irradia- 2 3 tion (up to 40 h). The DOM degradation of the TWW and synthetic solution has been analyzed by fluorescence 3D excita - tion emission matrix (3D EEM). Synergistic effect was expected and it was found that the rate of decrease of fluorescence intensity increased with time. Within 20 h, for the synthetic solution, reduction of fluorescence intensity (80%) reaches an equilibrium. In contrast, the rate of decrease in the fluorescence intensity is highest (91%) in 40 h of irradiation for TWW. This reduction of fluorescence intensity indicates the degradation of DOM and can be expressed well by second-order model kinetics. Reduction of TOC, BOD and COD load again validated the degradation of DOM from TWW by catalyst F e O 5 2 3 NPs-induced solar irradiation. We applied the treated wastewater on the plant to observe the reusability of the treated TWW, and the morphological data analysis of the plant demonstrates that the catalyst F e O NPs-induced solar-irradiated wastewater 2 3 exhibits less adverse impact on plant morphology. Keywords Iron nanoparticle · Textile wastewater · 3D EEM Introduction matter (DOM) concentration (Paul et al. 2012). According to the World Bank estimation, textile dyeing and finishing The textile industry is the main creator of effluent wastewa - treatment given to a fabric generates around 17–20% of ter in Bangladesh, due to a greater consumption of water industrial wastewater (Kant 2012). Selection of the suitable for its different wet and dye processing operations. This method and material for the sustainable textile wastewa- effluent wastewater has been recognized to have high color, ter (TWW) treatment is a highly complex task, where we high BOD and COD load, as well as high dissolved organic have to consider four factors, quality standard to be met, the treatment efficiency, the cost of treatment and also the reusability of the treated water (Huang et al. 2008; Zhang and Fang 2010; Oller et al. 2011). In an effort to combat the * Fahmida Parvin fahmidaprvn497@gmail.com problem of water pollution, rapid and significant progresses in wastewater treatment have been made, including photo- Department of Environmental Sciences, Jahangirnagar catalytic oxidation, adsorption/separation processing and University, Savar, Dhaka 1342, Bangladesh bioremediation (Long et al. 2011; Pang et al. 2011; Parvin Graduate School of Environmental Science, Hokkaido et al. 2015, 2017). However, their applications have been University, Sapporo 060-0819, Japan restricted by many factors, such as processing efficiency, Department of Environmental Science and Engineering, operational method, energy requirements and economic ben- Ewha Womans University, Seoul 03760, Republic of Korea efit. Recently, nanomaterials (NMs) have been suggested to Department of Environmental Science, Bangladesh be efficient, cost-effective and environmental friendly alter - University of Professionals, Mirpur Cantonment, native to existing treatment materials, from the standpoints Dhaka 1216, Bangladesh Vol.:(0123456789) 1 3 73 Page 2 of 11 Applied Water Science (2018) 8:73 of both resource conservation and environmental remedia- organic molecules with chromophoric (light absorbing) and tion (Dimitrov 2006; Dastjerdi and Montazer 2010). fluorophoric (light emitting) moieties (Wang et al. 2009 ). Degradation of DOM and azo dye of water using semi- Therefore, three-dimensional excitation emission matrix conductor oxide nanomaterials-based photocatalysts is (3DEEM) fluorescence spectroscopy has been widely used a useful process, where pollutants are mineralized by the to detect detailed changes and transformations of organic photocatalytic mechanism (Akhavan and Azimirad 2009). matter in wastewater (Wang et al. 2009). Photocatalysis refers to the rate of photoreactions (oxidation/ In this study, Fe O NPs have been synthesized and, for 2 3 reduction) brought on by the activation of a catalyst, usually the first time, the efficacy of Fe O NPs as a photocatalyst 2 3 a semiconductor oxide, through illumination under ultravio- under solar irradiation in degrading DOM from synthetic let (UV) or visible light. The direct band-gap excitation of dye (Procion blue) solution and TWW has been observed semiconductors generates electron–hole pairs, which partici- using fluorescence spectroscopy and characterized by pate in reduction and oxidation processes. Among numer- 3DEEM. Additionally, the effect of the degraded wastewa- ous oxide semiconductor photocatalysts (e.g., TiO, ZrO , ter on plant growth has also been studied to check the reus- 2 2 ZnO, MoO, SnO , α-Fe O ), anatase crystalline forms of ability of TWW. 3 2 2 3 Fe O and TiO nanomaterial are suitable photocatalysts, 2 3 2 as those are nontoxic and have vigorous oxidizing capacity (Park and Choi 2004; Nagaveni et al. 2004; Zou et al. 2001). Experimental However, one limitation of T iO is that it mainly absorbs UV light, which covers only 4–6% of the solar spectrum. In this Synthesis of  Fe O NPs 2 3 regard, iron oxide nanoparticle (F e O NP) with band gap 2 3 around 2.3 eV is a suitable candidate to absorb solar light, We synthesized the Fe O NPs according to the method 2 3 greater surface area and be used as a photocatalyst. described in Rahman et al. (2011). In brief, both F eCl and Akhavan and Azimirad (2009) use mercury lamp as a urea were slowly dissolved in de-ionized water separately source of visible light prior to investigating the effect of at room temperature to make 0.5 M concentration of FeCl semiconductor nanocatalyst in dye removal and wastewater and urea solution. Then the solutions were mixed gently treatment. However, using this kind of source is not viable and stirred until the two solutions mixed properly. The pH in pilot-scale work or in practical application. Hence, use of the solution was adjusted using ammonia solution drop- of direct sunlight is more practicable (Bishnoi et al. 2018) wise to approximately 9.66. Then the mixture was put into a because of its availability. In addition, because of the geo- hydrothermal cell (Teflon line autoclave) to be placed in an graphical position of Bangladesh, total solar insolation that oven for 6 h at 150 °C. Then the solution was washed with reaches different locations of Bangladesh vary from 4 to 5 acetone and kept for drying at room temperature (Rahman kWh/m /day, whereas the global solar insolation varies from et al. 2011). 3.8 to 6.4 kW h/m /day (Nandi et al. 2012). Thus consider- ing the fact, it is wise to use direct sunlight to elucidate the Characterization of  Fe O NPs 2 3 effect of nano-photocatalyst. Recently, Fe-doped TiO photocatalysts and Fe O –TiO The structural and optical properties of the synthesized 2 2 3 2 coupled semiconductor photocatalysts have been designed Fe O NPs were tested. The λ-max of the synthesized iron 2 3 for photodegradation of toxic and organic pollutant sub- particles was measured using UV/visible spectrophotome- stances in visible light (Akhavan and Azimirad 2009). ter (Shimadzu, Model no: mini-1240). The IR spectra were However, we always look for those techniques which are measured by FTIR spectrophotometer (Shimadzu, Model inexpensive and easy to prepare. Hence, several laboratories no-IR Prestige 21) to study the structural properties of have examined the efficiency of Fe O NPs (without doping) the NPs. The FTIR spectrum was taken in a transmittance 2 3 −1 during the photocatalytic purification of dye mixed water mode. The spectra were obtained at a resolution of 4 cm −1 (Bandra et al. 2001; Cunningham et al. 1988; Fernandez in the range of 400–4000 cm in KBr media. The surface et al. 1998). However, another big problem in wastewater morphology of the synthesized Fe O NPs was assessed by 2 3 is DOM. The presence of DOM not only affects the current a scanning electron microscope (SEM) (JSM-630 JEOL, discharge standards, but also presents significant challenges Japan). in wastewater reclamation (Gou et al. 2011). DOM contains large amounts of unsaturated and aromatic structures with Wastewater sampling and photocatalytic irradiation different functional groups that have fluorescence character - istics, which allows for the utilization of fluorescence spec- TWW used in this work was sampled from a textile industry troscopy to extract information on the degradation of DOM named Pakiza Group Ltd., which is situated at Savar, Bang- at the time of TWW treatment. In particular, DOM includes ladesh. The sample was a mixture of wastewater, discharged 1 3 Applied Water Science (2018) 8:73 Page 3 of 11 73 from 225 to 500 nm in 5 nm steps, and the emitted fluo- rescence detected between 240 and 600 nm in 2 nm steps. Excitation and emission slit widths were 5 nm. Scan speed was 1200 nm/min, permitting collection of a complete EEM in 18 min. Excitation emission matrix (EEM) data were cali- brated by normalization to water Raman scattering. Physicochemical parameter of TWW Changes in the environmentally important parameters (BOD, COD, TOC) of the TWW after solar irradiation (both in the presence and absence of catalyst F e O NPs) were analyzed. 2 3 The 5-day BOD test of the samples was conducted accord- Fig. 1 Solar irradiation of water samples in the presence of Fe O 2 3 ing to the standard method (ASTM-5210 B). The COD of NPs the samples was determined by the closed reflux colorimet - ric method (ASTM-5220 D). Total organic carbon (TOC) from several sections such as washing, dying, waxing and was measured by the high temperature catalytic oxidation rinsing. The samples (40 ml) were then exposed to solar method with a TOC 5000A (Shimadzu, Japan) using potas- radiation for up to 40 h (10 days: every day 4 h, from 10 AM sium hydrogen phthalate (KHP) as a standard (Tareq et al. to 2 PM) (both in the presence and absence of catalyst Fe O 2013). 2 3 NPs) as explained in Bishnoi et al. (2018). Here, a constant catalyst (Fe O NPs) concentration (5 mg/L) was used. The Analysis of the effect of treated wastewater in plant 2 3 water samples were kept in vials by adding F e O NPs and growth 2 3 sealed with cap to avoid evaporation of water (Fig. 1). We conducted this study in February at the rooftop of our labo- The treated and raw textile wastewaters were irrigated into ratory, when the solar insolation for Dhaka was reported Malabar spinach to observe the effect of solar-irradiated tex- to be 4.79 kWh/m (Nandi et al. 2012). Similar procedures tile wastewaters on plant growth using pot experiments. For were also applied for the synthetic dye (Procion blue) solu- this purpose, the real TWW was solar irradiated without any tion. We used 40 mL of synthetic solutions (50 mg/L of dye) dilution both in presence of catalyst iron oxide nanoparticles and added 5 mg/L Fe O NPs. This dye was purchased from in a glass reactor which containing at least 7 l of wastewa- 2 3 Sigma-Aldrich. The properties of the Procion blue (PB) dye ter at a time and catalyst (Fig. 2). Every day, 1 l of water are as follows: samples (treated and untreated) was poured on the soil of each pot, where the plant was sown, as described in Parvin • Linear formula: C H Cl N O S et al. (2015). Four pots of Malabar spinach (3 replications) 23 14 2 6 8 2. Molecular weight: 637.437. were prepared by adding garden soil with the appropriate • Lambda max: 607 nm. moisture content and successively nourished with water, MDL number: MFCD00001218. raw and treated textile wastewater. Every week, the plants were monitored prior to measuring the plant morphology to Characterization of the degraded wastewater Fluorescent dissolved organic matter degradation study The rate of degradation of DOM in dye solution and TWW after photocatalytic solar irradiation was studied by a fluo- rescence spectrophotometer (F-4600, HITACHI, Tokyo, Japan) by a method described in Tareq et  al. 2013 and Yamashita and Tanoue 2003. Briefly, all the samples were filtered through a glass-fiber membrane (0.45 μm) to remove suspended materials that may react with DOM. Excitation emission matrices (EEMs) were created using FL Solutions software. Before analysis, water samples were diluted 1000 times to keep the spectra within the upper limit of analysis. Fig. 2 Solar irradiation of textile wastewater samples in the presence To generate an EEM, excitation wavelengths were scanned of Fe O NPs for irrigating on plants 2 3 1 3 73 Page 4 of 11 Applied Water Science (2018) 8:73 compare the effect of treated textile effluent with the raw and where Ebg is the band-gap energy and λ is the wavelength max control one. At 45 DAS (days after sowing) the plants were (444.0 nm) of the NPs. harvested and the lengths of roots and dry mass were meas- FTIR, an excellent tool for recognizing the types of ured. The morphology of the plants was measured according chemical bonds in a molecule, was recorded for F e O NPs 2 3 to the method described in Parvin et al. (2013, 2015). (Fig. 3). It displays several bands at 447, 561, 935, 1400, −1 1630, 1751 and 3134 cm and it is known from the literature that Fe O NPs give absorption bands at those wavelengths 2 3 Results and discussion (Rahman et al. 2011; Ma and Qi 2007). The band observed at 447.49 and 561.29 represents Fe–O–Fe stretching vibra- Characterizations of  Fe O NPs tion, and these vibration bands at low frequency regions 2 3 indicate the formation of Fe O NPs. The vibration bands 2 3 −1 The optical property of the Fe O NPs is one of the signifi- observed at 1400 and 1630 cm are assigned to O=C=O 2 3 cant properties for determining its optical and photocatalytic stretching and OH bending vibration. The band observed at −1 activity. The absorption spectrum of as-grown Fe O NPs 1751.36 cm represents the C=O stretching of carbonyl. 2 3 −1 solution was measured by UV–visible spectrophotometer The strong absorption band at 3032 and 3134.33 cm rep- and an onset of absorption maxima was found at 444.0 nm resents the C–H stretching vibration of alkanes and alkenes. in the visible range (200–800) nm wavelength. The lambda Rahman et al. (2011) reported that, the absorption bands at maxima of the synthesized NPs are quite similar to those these wavelengths normally arise from the carbon dioxide reported by Cornell and Schwertmann (2003) and Rahman and water which usually nanomaterials absorbed from the et al. (2011) and this wavelength indicates the formation environment due to their mesoporous structure. of Fe O NPs. Band-gap energy is calculated on the basis The SEM image has been used here to verify the particle 2 3 of the maximum absorption band (444 nm) of Fe O NPs. size and morphology of Fe O NPs. Figure 4 shows that the 2 3 2 3 The band-gap energy of NPs was 2.792 eV, according to the different diameters of NPs grown by the hydrothermal pro- following equation: cess possessed almost uniform spherical shape. The particles are aggregated with small crystals with a broad size distribu- Ebg = (eV), tion up to 500 nm (Fig. 4a) and grown at a very high density. Fig. 3 FTIR spectra of F e O NPs 2 3 1 3 Applied Water Science (2018) 8:73 Page 5 of 11 73 Fig. 4 High- to low-resolution SEM image of Fe O NPs 2 3 From this figure, it is clear that the synthesized material is an NP and the morphology of the synthesized iron dioxide NPs is identical. The diameter of the synthesized iron NPs is found in the range of 56–83 nm (Fig.  4b), whereas the average diameter of Fe O NPs is close to 71 nm (Rahman 2 3 et al. 2011). From those analyses, it is clear that F e O NPs 2 3 has been properly synthesized. Synergistic effect of  Fe O NPs in the presence 2 3 of solar radiation for the degradation of DOM from textile wastewater Study of fluorescence intensity The occurrence of dissolved organic matter is rather com- mon in dye-containing industrial wastewater. Given that Fe O with a band gap of 2.3–2.7 eV (Akhavan and Azi- 2 3 mirad 2009) is an n-type semiconducting material and a suitable candidate for photodegradation of dye compounds under visible light condition and consequently degradation of DOM, we examined the synergistic effect of Fe O NPs 2 3 under solar radiation for the degradation of DOM of dye (PB) solution and TWW (Fig. 5a, b) by means of fluores- cence intensity. In the case of synthetic dye (PB) solution Fig. 5 Time-dependent changes in fluorescence intensity at (Fig. 5a), the reduction in fluorescence intensity reaches in 350 nm/450 nm of the PB dye and TWW equilibrium (80%) within 20 h of solar irradiation. When Fe O NPs are illuminated under visible light, electrons from 2 3 the valence band jump into the conduction band, causing Kasiri 2010) and in a consequent degradation of DOM. For generation of electrons and positively charged holes and TWW, the reduction in fluorescence intensity increases with leading to the formation of active oxidation species, which increase in time (Fig. 5b). Maximum reduction (91%) was are responsible for enhanced DOM degradation. Generally, achieved on 40 h of irradiation. the sites near the chromophore (for instance, C–N=N– bond) To investigate the kinetic mechanism of DOM degra- is the attacked area in the photocatalytic degradation pro- dation, we looked for the reaction kinetics. We elucidated cess, and photocatalytic destruction of the C–N=and the reaction kinetics using the fluorescence intensity (a.u.) –N=N– bonds leads to fading of the dyes (Khataee and from 3D EEMs against time, as the fluorescence intensity is 1 3 73 Page 6 of 11 Applied Water Science (2018) 8:73 thought to be proportional to the concentration of the analyte the rate of degradation reaches an equilibrium stage. We (Wang et al. 2009). The first-order reaction rate constant calculate the half-life (t ) of second-order reactions using 1/2 for the reaction was determined by fitting the fluorescence the following equation: intensities of the samples to the first-order equation: t = , 1∕2 Ln(I )= −k t + Ln(I ), (k × I ) t 1 0 2 o where I and I are the fluorescence intensities at time t and t 0 and the t of Pb dye is 5.02  h. As for TWW, the t is 1/2 1/2 at the initial time. k is the first-order rate constant. k and 1 1 2.99 h. I were calculated from the slope and intercept of the plots 0.cal of Ln(I ) vs. t. As for the second-order kinetics, the model can be expressed by the following equation: 3D EEM analysis 1 1 = k t + , I I t 0 To examine the extent of DOM degradation in synthetic where k is the second-order rate constant and k and I dye solutions and TWW by F e O NPs-induced solar irra- 2 2 0.cal 2 3 were calculated from the slope and intercept of the plots diation, 3D excitation emission matrices (EEMs) were cre- of 1/I vs. t. The first- and second-order model kinetics of ated by determining three fluorescent parameters (excita- DOM degradation of PB dye and TWW are given in Fig. 6. tion wavelength, emission wavelength, and the intensity of For both the dye solutions and TWW, the experimental data fluorescence) (Yamashita and Tanoue 2003 ). The results show relatively lower correlation (R = 0.89–0.96) in the are arranged in a grid (excitation × emission × intensity). first-order rate expressions (Fig.  6a, c). In contrast, a high The specific excitation and emission wavelengths are char - degree of linearity and high correlation (R = 0.99) with the acteristics of a particular molecular conformation (i.e., experimental data were found for second-order rate expres- fluorophore) that can indicate the composition of organic sion (Fig. 6b, d). These results suggest that the second-order compounds. Thus, the measured fluorescent peak inten- −1 kinetic model is best fitted for describing the DOM degrada - sity (Raman unit, nm ) of DOM is directly related to the tion from the dye solution, as well as from TWW and the concentration of the responsible fluorophore in the sample DOM degraded by bimolecular reaction. Here, in Fig. 6a, (Henderson et al. 2009). Here, the rate of DOM degradation b, the kinetics for synthetic dye (PB) solution was shown increases with increase in irradiation time and we get the for up to 20 h. As this is a pure dye solution, within 20 h best result for 40 h of irradiation for TWW. However, in the Fig. 6 First-order (a, c) and second-order (b, d) kinetics of the degradation DOM of PB dye and TWW with Fe O NPs 2 3 under visible light irradiation 1 3 Applied Water Science (2018) 8:73 Page 7 of 11 73 dye solution the rate of degradation reaches in equilibrium some means coupled with fluorophores excited at shorter within 20 h. Hence, we show the degradation of fluorescent wavelength can also cause redshift in the excitation emis- DOM using 3DEEM of synthetic dye solution and TWW sion spectra (Coble et al. 2014). If two double bonds are only at 20 and 40 h of irradiation, respectively (Figs. 7, 8). separated by a single bond, the double bonds are termed The fluorescence intensity of the synthetic dye (PB) conjugated. Conjugation of double bonds further induces a solution was close to 0.17RU, which decreased to 0.04RU redshift in the absorption (a so-called bathochromic shift). after 20 h of photodegradation (Fig. 7a, b). As for TWW, From uo fl rescence spectra analysis, it is clear that irradiation after solar irradiation the relative fluorescence intensity for 40 h gives best results for TWW. Hence, irradiation for has also decreased (from RU 0.17 to RU 0.10) (Fig. 8). In 40 h was chosen for further analysis with TWW. wastewater samples, the fluorescence peak at around Ex/ Em = 390–440 nm/442–508 nm indicates the humic sub- Reduction in TOC, COD and BOD of TWW stances (Table 1), which is the specific fluorescence indica- after catalyst‑induced solar irradiation tor of azo dye in TWW (Li et al. 2015). Additionally, two other peaks at around Ex/Em = 300–315 nm/380–382 nm Fluorescence data of wastewater as well as treated wastewater indicate the protein-like materials and the peak at around are thought to well correlate with other parameters including Ex/Em = 270–295 nm/350–362 nm indicates fulvic acid. biochemical oxygen demand (BOD), chemical oxygen demand The synergistic effect of Fe O NPs-induced solar irradia- (COD) and total organic carbon (TOC) (Reynolds 2002). In 2 3 tion caused a redshift in excitation emission wavelength addition, removal of dyes also reduces BOD, COD and TOC of all organic matters and the fluorescence intensity also of wastewater. Hence, to validate the degradation of DOM of decreased (Table  1). The resulting redshift could be due TWW under solar irradiation in the presence of Fe O NPs, 2 3 to the destruction of various fluorophores (all absorbing we also measure the environmentally important parameters at long wavelength) via indirect photochemistry excited at (BOD , COD and TOC) of TWW. Table 2 represents the per- long wavelength. In addition, destruction of fluorophores cent removal of TOC, COD and BOD of TWW after catalyst- by direct photochemistry excited at both wavelength or by induced solar irradiation (40 h). The BOD, COD and TOC of Fig. 7 A representative illustration of the three-dimensional excitation emission matrix (3DEEM) fluorescence spectra of PB dye solution. a Raw solution, b at 20 h of irradiation in the presence of Fe O NPs 2 3 1 3 73 Page 8 of 11 Applied Water Science (2018) 8:73 Fig. 8 A representative illustration of three-dimensional excitation emission matrix (3DEEM) fluorescence spectra of wastewater. a Raw waste- water, b at 40 h of irradiation in the presence of Fe O NPs 2 3 Table 1 Fluorescence properties Samples Peak intensities with coordinates (excitation/emission wavelengths) of Procion blue dye and textile wastewater Peak 1 Peak 2 Peak 3 Procion blue dye solution  Raw 0.06 (375 nm/460 nm) 0.07 (365 nm/452 nm) 0.02 (295 nm/354 nm)  Fe O induced 0.007 (380 nm/432 nm) 0.01 (340 nm/434 nm) 0.01 (280 nm/308 nm) 2 3 solar irradiated for 20 h days Textile wastewater  Raw 0.01 (390 nm/442 nm) 0.01 (300 nm/380 nm) 0.01 (270 nm/350 nm)  Fe O induced 0.008 (440 nm/508 nm) 0.009 (315 nm/382 nm) 0.01 (295 nm/362 nm) 2 3 solar irradiated for 40 h Table 2 Reduction in TOC, COD and BOD of real textile wastewater TWW are 208, 409 and 89 mg/L, respectively. Data in Table 2 after the treatment process (40 h) indicates that all those properties were improved after 40 h of solar irradiation with catalyst Fe O NPs. After 40 h of pho- BOD (%) COD (%) TOC (%) 2 3 tocatalytic irradiation, TOC, COD and BOD were reduced by After catalyst-induced solar irradia- 37.89 44.68 42.2 42.2, 44.68 and 37.89%, respectively. By the influence of solar tion days irradiation in the presence of Fe O NPs, complex organic 2 3 compounds are converted to simple compounds such as carbon dioxide, water, nitrate, amide and carboxylic acids (Hussein and Abbas 2010; Xu et al. 2012) and consequently the BOD, COD load and TOC of TWW are decreased. This result again 1 3 Applied Water Science (2018) 8:73 Page 9 of 11 73 proves the degradation of DOM from TWW using Fe O NPs 2 3 under solar irradiation. However, the improvement rate is less in comparison to some other treatment, i.e., at 10 kGy direct gamma irradiation, the BOD and COD of TWW reduced by 59 and 61%, respectively (Parvin et al. 2015). These rates of reduction (Table 2) suggest that degradation compounds, especially low molecular weight aldehydes and organic acids, still remain in solution. So, it is recommended that, to achieve complete mineralization, a little higher concentration of Fe O 2 3 NPs in wastewater is necessary. Eec ff t of degraded wastewater on plant growth Textile wastewaters are thought to hinder plant growth (Parvin et al. 2015), as the water quality is worse compared to the standard for use for irrigation purpose. Hence, the treated wastewater was irrigated to plants to compare the effect of treated wastewater on plant growth with raw waste- water. Figure 9 represents the morphological parameter of Malabar spinach nourished by water (control), TWW and catalyst-induced solar-irradiated TWW (TWW1), respec- tively. The morphological data (e.g., plant height, number of leaves, root length and dry mass) given in Fig. 9 were meas- ured after 45 days as shown. As expected, plants irrigated by TWW showed very low morphological properties in comparison with plants treated with normal water, because wastewaters having low DO, higher concentration of DOM and BOD load hinder plant growth. However, when we nour- ish the plants with catalyst-induced solar-irradiated waste- water, the value of plant growth becomes higher, though Fig. 9 Morphological properties of Malabar spinach after irrigation with water (control), wastewater (TWW) and catalyst-induced irradi- these values of plant morphology are still less in compari- ated wastewater (TWW1) son to the values of the control. However, in our previous work (Parvin et al. 2015), we decolorized TWW, using ion- linearly increased with time and the best results were izing gamma irradiation, which showed a fertilizing effect on plant growth. The possible explanation is solar radiation found at 40  h of solar irradiation for TWW. As for Pb dye solution of 50 mg/L concentration, the rate of deg- is not so intense like the most penetrating ionizing gamma irradiation to break the azo dye completely into nitrogen radation (80%) reached in equilibrium within 20 h using 5 mg/l Fe O NPs. The degradation of fluorescent DOM and ammonia, which is the reason for suppressing the plant 2 3 growth (though little), instead of acting as a fertilizer. How- of textile wastewater and dye solution by means of fluores- cence intensity can be described well by the second-order ever, using solar radiation is cost-effective and renewable compared to gamma radiation, as gamma radiation plants kinetic model. Analysis of 3DEEM revealed that, after photocatalytic irradiation, the intensity of humic acid is require high maintenance cost and the source Co is not renewable. Hence, the use of a relatively high concentration reduced, which is the main florescence indicator of azo dye in TWW. The degradation of DOM is again supported by of Fe O NPs (more than 5 mg/l) to accelerate the degrada- 2 3 tion ability of solar radiation is recommended in degrading the reduction of BOD, COD and TOC of TWW, indicating the applicability of this method (use of nanocatalyst under the dye and DOM completely. sunlight) in open lagoon/pond of the textile wastewater treatment plant. The catalyst-induced solar-irradiated Conclusions wastewater is found to have less effect on plant growth compared to raw wastewater. However, a little higher con- We synthesized properly Fe O NPs and it has also been centration of Fe O NPs is recommended for the complete 2 3 2 3 degradation of DOM. Hence, in our next work, we will proved by UV–Vis, FTIR spectra and SEM images analy- sis. Degradation of DOM of the dye solution and TWW focus on catalyst Fe O NPs concentration-dependent dye 2 3 1 3 73 Page 10 of 11 Applied Water Science (2018) 8:73 Khataee AR, Kasiri MB (2010) Photocatalytic degradation of organic and the DOM degradation of synthetic dye solution and dyes in the presence of nanostructured titanium dioxide: Influ- TWW. ence of the chemical structure of dyes. J Mol Catal A Chem 328(1–2):8–26. https ://doi.org/10.1016/j.molca ta.2010.05.023 Open Access This article is distributed under the terms of the Crea- Li WT, Xu ZX, Wu Q, Li Y, Shuang CD, Li AM (2015) Characteri- tive Commons Attribution 4.0 International License (http://creat iveco zation of fluorescent dissolved organic matter and identification mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- of specific fluorophores in textile effluents. 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Facile synthesis of iron oxide nanoparticle and synergistic effect of iron nanoparticle in the presence of sunlight for the degradation of DOM from textile wastewater

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Earth Sciences; Hydrogeology; Water Industry/Water Technologies; Industrial and Production Engineering; Waste Water Technology / Water Pollution Control / Water Management / Aquatic Pollution; Nanotechnology; Private International Law, International & Foreign Law, Comparative Law
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2190-5487
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2190-5495
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10.1007/s13201-018-0719-5
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Abstract

This study explores the capacity of synthesized F e O nanoparticles (NPs) under sunlight for the degradation of dissolved 2 3 organic matter (DOM) from synthetic (Procion blue dye) solution as well as from textile wastewater (TWW). Fe O NPs were 2 3 properly synthesized and confirmed by UV absorbance, FTIR spectra and SEM image analysis. Photocatalytic degradation of DOM from TWW and synthetic solution was performed by catalyst F e O NPs (5 mg/L) in the presence of solar irradia- 2 3 tion (up to 40 h). The DOM degradation of the TWW and synthetic solution has been analyzed by fluorescence 3D excita - tion emission matrix (3D EEM). Synergistic effect was expected and it was found that the rate of decrease of fluorescence intensity increased with time. Within 20 h, for the synthetic solution, reduction of fluorescence intensity (80%) reaches an equilibrium. In contrast, the rate of decrease in the fluorescence intensity is highest (91%) in 40 h of irradiation for TWW. This reduction of fluorescence intensity indicates the degradation of DOM and can be expressed well by second-order model kinetics. Reduction of TOC, BOD and COD load again validated the degradation of DOM from TWW by catalyst F e O 5 2 3 NPs-induced solar irradiation. We applied the treated wastewater on the plant to observe the reusability of the treated TWW, and the morphological data analysis of the plant demonstrates that the catalyst F e O NPs-induced solar-irradiated wastewater 2 3 exhibits less adverse impact on plant morphology. Keywords Iron nanoparticle · Textile wastewater · 3D EEM Introduction matter (DOM) concentration (Paul et al. 2012). According to the World Bank estimation, textile dyeing and finishing The textile industry is the main creator of effluent wastewa - treatment given to a fabric generates around 17–20% of ter in Bangladesh, due to a greater consumption of water industrial wastewater (Kant 2012). Selection of the suitable for its different wet and dye processing operations. This method and material for the sustainable textile wastewa- effluent wastewater has been recognized to have high color, ter (TWW) treatment is a highly complex task, where we high BOD and COD load, as well as high dissolved organic have to consider four factors, quality standard to be met, the treatment efficiency, the cost of treatment and also the reusability of the treated water (Huang et al. 2008; Zhang and Fang 2010; Oller et al. 2011). In an effort to combat the * Fahmida Parvin fahmidaprvn497@gmail.com problem of water pollution, rapid and significant progresses in wastewater treatment have been made, including photo- Department of Environmental Sciences, Jahangirnagar catalytic oxidation, adsorption/separation processing and University, Savar, Dhaka 1342, Bangladesh bioremediation (Long et al. 2011; Pang et al. 2011; Parvin Graduate School of Environmental Science, Hokkaido et al. 2015, 2017). However, their applications have been University, Sapporo 060-0819, Japan restricted by many factors, such as processing efficiency, Department of Environmental Science and Engineering, operational method, energy requirements and economic ben- Ewha Womans University, Seoul 03760, Republic of Korea efit. Recently, nanomaterials (NMs) have been suggested to Department of Environmental Science, Bangladesh be efficient, cost-effective and environmental friendly alter - University of Professionals, Mirpur Cantonment, native to existing treatment materials, from the standpoints Dhaka 1216, Bangladesh Vol.:(0123456789) 1 3 73 Page 2 of 11 Applied Water Science (2018) 8:73 of both resource conservation and environmental remedia- organic molecules with chromophoric (light absorbing) and tion (Dimitrov 2006; Dastjerdi and Montazer 2010). fluorophoric (light emitting) moieties (Wang et al. 2009 ). Degradation of DOM and azo dye of water using semi- Therefore, three-dimensional excitation emission matrix conductor oxide nanomaterials-based photocatalysts is (3DEEM) fluorescence spectroscopy has been widely used a useful process, where pollutants are mineralized by the to detect detailed changes and transformations of organic photocatalytic mechanism (Akhavan and Azimirad 2009). matter in wastewater (Wang et al. 2009). Photocatalysis refers to the rate of photoreactions (oxidation/ In this study, Fe O NPs have been synthesized and, for 2 3 reduction) brought on by the activation of a catalyst, usually the first time, the efficacy of Fe O NPs as a photocatalyst 2 3 a semiconductor oxide, through illumination under ultravio- under solar irradiation in degrading DOM from synthetic let (UV) or visible light. The direct band-gap excitation of dye (Procion blue) solution and TWW has been observed semiconductors generates electron–hole pairs, which partici- using fluorescence spectroscopy and characterized by pate in reduction and oxidation processes. Among numer- 3DEEM. Additionally, the effect of the degraded wastewa- ous oxide semiconductor photocatalysts (e.g., TiO, ZrO , ter on plant growth has also been studied to check the reus- 2 2 ZnO, MoO, SnO , α-Fe O ), anatase crystalline forms of ability of TWW. 3 2 2 3 Fe O and TiO nanomaterial are suitable photocatalysts, 2 3 2 as those are nontoxic and have vigorous oxidizing capacity (Park and Choi 2004; Nagaveni et al. 2004; Zou et al. 2001). Experimental However, one limitation of T iO is that it mainly absorbs UV light, which covers only 4–6% of the solar spectrum. In this Synthesis of  Fe O NPs 2 3 regard, iron oxide nanoparticle (F e O NP) with band gap 2 3 around 2.3 eV is a suitable candidate to absorb solar light, We synthesized the Fe O NPs according to the method 2 3 greater surface area and be used as a photocatalyst. described in Rahman et al. (2011). In brief, both F eCl and Akhavan and Azimirad (2009) use mercury lamp as a urea were slowly dissolved in de-ionized water separately source of visible light prior to investigating the effect of at room temperature to make 0.5 M concentration of FeCl semiconductor nanocatalyst in dye removal and wastewater and urea solution. Then the solutions were mixed gently treatment. However, using this kind of source is not viable and stirred until the two solutions mixed properly. The pH in pilot-scale work or in practical application. Hence, use of the solution was adjusted using ammonia solution drop- of direct sunlight is more practicable (Bishnoi et al. 2018) wise to approximately 9.66. Then the mixture was put into a because of its availability. In addition, because of the geo- hydrothermal cell (Teflon line autoclave) to be placed in an graphical position of Bangladesh, total solar insolation that oven for 6 h at 150 °C. Then the solution was washed with reaches different locations of Bangladesh vary from 4 to 5 acetone and kept for drying at room temperature (Rahman kWh/m /day, whereas the global solar insolation varies from et al. 2011). 3.8 to 6.4 kW h/m /day (Nandi et al. 2012). Thus consider- ing the fact, it is wise to use direct sunlight to elucidate the Characterization of  Fe O NPs 2 3 effect of nano-photocatalyst. Recently, Fe-doped TiO photocatalysts and Fe O –TiO The structural and optical properties of the synthesized 2 2 3 2 coupled semiconductor photocatalysts have been designed Fe O NPs were tested. The λ-max of the synthesized iron 2 3 for photodegradation of toxic and organic pollutant sub- particles was measured using UV/visible spectrophotome- stances in visible light (Akhavan and Azimirad 2009). ter (Shimadzu, Model no: mini-1240). The IR spectra were However, we always look for those techniques which are measured by FTIR spectrophotometer (Shimadzu, Model inexpensive and easy to prepare. Hence, several laboratories no-IR Prestige 21) to study the structural properties of have examined the efficiency of Fe O NPs (without doping) the NPs. The FTIR spectrum was taken in a transmittance 2 3 −1 during the photocatalytic purification of dye mixed water mode. The spectra were obtained at a resolution of 4 cm −1 (Bandra et al. 2001; Cunningham et al. 1988; Fernandez in the range of 400–4000 cm in KBr media. The surface et al. 1998). However, another big problem in wastewater morphology of the synthesized Fe O NPs was assessed by 2 3 is DOM. The presence of DOM not only affects the current a scanning electron microscope (SEM) (JSM-630 JEOL, discharge standards, but also presents significant challenges Japan). in wastewater reclamation (Gou et al. 2011). DOM contains large amounts of unsaturated and aromatic structures with Wastewater sampling and photocatalytic irradiation different functional groups that have fluorescence character - istics, which allows for the utilization of fluorescence spec- TWW used in this work was sampled from a textile industry troscopy to extract information on the degradation of DOM named Pakiza Group Ltd., which is situated at Savar, Bang- at the time of TWW treatment. In particular, DOM includes ladesh. The sample was a mixture of wastewater, discharged 1 3 Applied Water Science (2018) 8:73 Page 3 of 11 73 from 225 to 500 nm in 5 nm steps, and the emitted fluo- rescence detected between 240 and 600 nm in 2 nm steps. Excitation and emission slit widths were 5 nm. Scan speed was 1200 nm/min, permitting collection of a complete EEM in 18 min. Excitation emission matrix (EEM) data were cali- brated by normalization to water Raman scattering. Physicochemical parameter of TWW Changes in the environmentally important parameters (BOD, COD, TOC) of the TWW after solar irradiation (both in the presence and absence of catalyst F e O NPs) were analyzed. 2 3 The 5-day BOD test of the samples was conducted accord- Fig. 1 Solar irradiation of water samples in the presence of Fe O 2 3 ing to the standard method (ASTM-5210 B). The COD of NPs the samples was determined by the closed reflux colorimet - ric method (ASTM-5220 D). Total organic carbon (TOC) from several sections such as washing, dying, waxing and was measured by the high temperature catalytic oxidation rinsing. The samples (40 ml) were then exposed to solar method with a TOC 5000A (Shimadzu, Japan) using potas- radiation for up to 40 h (10 days: every day 4 h, from 10 AM sium hydrogen phthalate (KHP) as a standard (Tareq et al. to 2 PM) (both in the presence and absence of catalyst Fe O 2013). 2 3 NPs) as explained in Bishnoi et al. (2018). Here, a constant catalyst (Fe O NPs) concentration (5 mg/L) was used. The Analysis of the effect of treated wastewater in plant 2 3 water samples were kept in vials by adding F e O NPs and growth 2 3 sealed with cap to avoid evaporation of water (Fig. 1). We conducted this study in February at the rooftop of our labo- The treated and raw textile wastewaters were irrigated into ratory, when the solar insolation for Dhaka was reported Malabar spinach to observe the effect of solar-irradiated tex- to be 4.79 kWh/m (Nandi et al. 2012). Similar procedures tile wastewaters on plant growth using pot experiments. For were also applied for the synthetic dye (Procion blue) solu- this purpose, the real TWW was solar irradiated without any tion. We used 40 mL of synthetic solutions (50 mg/L of dye) dilution both in presence of catalyst iron oxide nanoparticles and added 5 mg/L Fe O NPs. This dye was purchased from in a glass reactor which containing at least 7 l of wastewa- 2 3 Sigma-Aldrich. The properties of the Procion blue (PB) dye ter at a time and catalyst (Fig. 2). Every day, 1 l of water are as follows: samples (treated and untreated) was poured on the soil of each pot, where the plant was sown, as described in Parvin • Linear formula: C H Cl N O S et al. (2015). Four pots of Malabar spinach (3 replications) 23 14 2 6 8 2. Molecular weight: 637.437. were prepared by adding garden soil with the appropriate • Lambda max: 607 nm. moisture content and successively nourished with water, MDL number: MFCD00001218. raw and treated textile wastewater. Every week, the plants were monitored prior to measuring the plant morphology to Characterization of the degraded wastewater Fluorescent dissolved organic matter degradation study The rate of degradation of DOM in dye solution and TWW after photocatalytic solar irradiation was studied by a fluo- rescence spectrophotometer (F-4600, HITACHI, Tokyo, Japan) by a method described in Tareq et  al. 2013 and Yamashita and Tanoue 2003. Briefly, all the samples were filtered through a glass-fiber membrane (0.45 μm) to remove suspended materials that may react with DOM. Excitation emission matrices (EEMs) were created using FL Solutions software. Before analysis, water samples were diluted 1000 times to keep the spectra within the upper limit of analysis. Fig. 2 Solar irradiation of textile wastewater samples in the presence To generate an EEM, excitation wavelengths were scanned of Fe O NPs for irrigating on plants 2 3 1 3 73 Page 4 of 11 Applied Water Science (2018) 8:73 compare the effect of treated textile effluent with the raw and where Ebg is the band-gap energy and λ is the wavelength max control one. At 45 DAS (days after sowing) the plants were (444.0 nm) of the NPs. harvested and the lengths of roots and dry mass were meas- FTIR, an excellent tool for recognizing the types of ured. The morphology of the plants was measured according chemical bonds in a molecule, was recorded for F e O NPs 2 3 to the method described in Parvin et al. (2013, 2015). (Fig. 3). It displays several bands at 447, 561, 935, 1400, −1 1630, 1751 and 3134 cm and it is known from the literature that Fe O NPs give absorption bands at those wavelengths 2 3 Results and discussion (Rahman et al. 2011; Ma and Qi 2007). The band observed at 447.49 and 561.29 represents Fe–O–Fe stretching vibra- Characterizations of  Fe O NPs tion, and these vibration bands at low frequency regions 2 3 indicate the formation of Fe O NPs. The vibration bands 2 3 −1 The optical property of the Fe O NPs is one of the signifi- observed at 1400 and 1630 cm are assigned to O=C=O 2 3 cant properties for determining its optical and photocatalytic stretching and OH bending vibration. The band observed at −1 activity. The absorption spectrum of as-grown Fe O NPs 1751.36 cm represents the C=O stretching of carbonyl. 2 3 −1 solution was measured by UV–visible spectrophotometer The strong absorption band at 3032 and 3134.33 cm rep- and an onset of absorption maxima was found at 444.0 nm resents the C–H stretching vibration of alkanes and alkenes. in the visible range (200–800) nm wavelength. The lambda Rahman et al. (2011) reported that, the absorption bands at maxima of the synthesized NPs are quite similar to those these wavelengths normally arise from the carbon dioxide reported by Cornell and Schwertmann (2003) and Rahman and water which usually nanomaterials absorbed from the et al. (2011) and this wavelength indicates the formation environment due to their mesoporous structure. of Fe O NPs. Band-gap energy is calculated on the basis The SEM image has been used here to verify the particle 2 3 of the maximum absorption band (444 nm) of Fe O NPs. size and morphology of Fe O NPs. Figure 4 shows that the 2 3 2 3 The band-gap energy of NPs was 2.792 eV, according to the different diameters of NPs grown by the hydrothermal pro- following equation: cess possessed almost uniform spherical shape. The particles are aggregated with small crystals with a broad size distribu- Ebg = (eV), tion up to 500 nm (Fig. 4a) and grown at a very high density. Fig. 3 FTIR spectra of F e O NPs 2 3 1 3 Applied Water Science (2018) 8:73 Page 5 of 11 73 Fig. 4 High- to low-resolution SEM image of Fe O NPs 2 3 From this figure, it is clear that the synthesized material is an NP and the morphology of the synthesized iron dioxide NPs is identical. The diameter of the synthesized iron NPs is found in the range of 56–83 nm (Fig.  4b), whereas the average diameter of Fe O NPs is close to 71 nm (Rahman 2 3 et al. 2011). From those analyses, it is clear that F e O NPs 2 3 has been properly synthesized. Synergistic effect of  Fe O NPs in the presence 2 3 of solar radiation for the degradation of DOM from textile wastewater Study of fluorescence intensity The occurrence of dissolved organic matter is rather com- mon in dye-containing industrial wastewater. Given that Fe O with a band gap of 2.3–2.7 eV (Akhavan and Azi- 2 3 mirad 2009) is an n-type semiconducting material and a suitable candidate for photodegradation of dye compounds under visible light condition and consequently degradation of DOM, we examined the synergistic effect of Fe O NPs 2 3 under solar radiation for the degradation of DOM of dye (PB) solution and TWW (Fig. 5a, b) by means of fluores- cence intensity. In the case of synthetic dye (PB) solution Fig. 5 Time-dependent changes in fluorescence intensity at (Fig. 5a), the reduction in fluorescence intensity reaches in 350 nm/450 nm of the PB dye and TWW equilibrium (80%) within 20 h of solar irradiation. When Fe O NPs are illuminated under visible light, electrons from 2 3 the valence band jump into the conduction band, causing Kasiri 2010) and in a consequent degradation of DOM. For generation of electrons and positively charged holes and TWW, the reduction in fluorescence intensity increases with leading to the formation of active oxidation species, which increase in time (Fig. 5b). Maximum reduction (91%) was are responsible for enhanced DOM degradation. Generally, achieved on 40 h of irradiation. the sites near the chromophore (for instance, C–N=N– bond) To investigate the kinetic mechanism of DOM degra- is the attacked area in the photocatalytic degradation pro- dation, we looked for the reaction kinetics. We elucidated cess, and photocatalytic destruction of the C–N=and the reaction kinetics using the fluorescence intensity (a.u.) –N=N– bonds leads to fading of the dyes (Khataee and from 3D EEMs against time, as the fluorescence intensity is 1 3 73 Page 6 of 11 Applied Water Science (2018) 8:73 thought to be proportional to the concentration of the analyte the rate of degradation reaches an equilibrium stage. We (Wang et al. 2009). The first-order reaction rate constant calculate the half-life (t ) of second-order reactions using 1/2 for the reaction was determined by fitting the fluorescence the following equation: intensities of the samples to the first-order equation: t = , 1∕2 Ln(I )= −k t + Ln(I ), (k × I ) t 1 0 2 o where I and I are the fluorescence intensities at time t and t 0 and the t of Pb dye is 5.02  h. As for TWW, the t is 1/2 1/2 at the initial time. k is the first-order rate constant. k and 1 1 2.99 h. I were calculated from the slope and intercept of the plots 0.cal of Ln(I ) vs. t. As for the second-order kinetics, the model can be expressed by the following equation: 3D EEM analysis 1 1 = k t + , I I t 0 To examine the extent of DOM degradation in synthetic where k is the second-order rate constant and k and I dye solutions and TWW by F e O NPs-induced solar irra- 2 2 0.cal 2 3 were calculated from the slope and intercept of the plots diation, 3D excitation emission matrices (EEMs) were cre- of 1/I vs. t. The first- and second-order model kinetics of ated by determining three fluorescent parameters (excita- DOM degradation of PB dye and TWW are given in Fig. 6. tion wavelength, emission wavelength, and the intensity of For both the dye solutions and TWW, the experimental data fluorescence) (Yamashita and Tanoue 2003 ). The results show relatively lower correlation (R = 0.89–0.96) in the are arranged in a grid (excitation × emission × intensity). first-order rate expressions (Fig.  6a, c). In contrast, a high The specific excitation and emission wavelengths are char - degree of linearity and high correlation (R = 0.99) with the acteristics of a particular molecular conformation (i.e., experimental data were found for second-order rate expres- fluorophore) that can indicate the composition of organic sion (Fig. 6b, d). These results suggest that the second-order compounds. Thus, the measured fluorescent peak inten- −1 kinetic model is best fitted for describing the DOM degrada - sity (Raman unit, nm ) of DOM is directly related to the tion from the dye solution, as well as from TWW and the concentration of the responsible fluorophore in the sample DOM degraded by bimolecular reaction. Here, in Fig. 6a, (Henderson et al. 2009). Here, the rate of DOM degradation b, the kinetics for synthetic dye (PB) solution was shown increases with increase in irradiation time and we get the for up to 20 h. As this is a pure dye solution, within 20 h best result for 40 h of irradiation for TWW. However, in the Fig. 6 First-order (a, c) and second-order (b, d) kinetics of the degradation DOM of PB dye and TWW with Fe O NPs 2 3 under visible light irradiation 1 3 Applied Water Science (2018) 8:73 Page 7 of 11 73 dye solution the rate of degradation reaches in equilibrium some means coupled with fluorophores excited at shorter within 20 h. Hence, we show the degradation of fluorescent wavelength can also cause redshift in the excitation emis- DOM using 3DEEM of synthetic dye solution and TWW sion spectra (Coble et al. 2014). If two double bonds are only at 20 and 40 h of irradiation, respectively (Figs. 7, 8). separated by a single bond, the double bonds are termed The fluorescence intensity of the synthetic dye (PB) conjugated. Conjugation of double bonds further induces a solution was close to 0.17RU, which decreased to 0.04RU redshift in the absorption (a so-called bathochromic shift). after 20 h of photodegradation (Fig. 7a, b). As for TWW, From uo fl rescence spectra analysis, it is clear that irradiation after solar irradiation the relative fluorescence intensity for 40 h gives best results for TWW. Hence, irradiation for has also decreased (from RU 0.17 to RU 0.10) (Fig. 8). In 40 h was chosen for further analysis with TWW. wastewater samples, the fluorescence peak at around Ex/ Em = 390–440 nm/442–508 nm indicates the humic sub- Reduction in TOC, COD and BOD of TWW stances (Table 1), which is the specific fluorescence indica- after catalyst‑induced solar irradiation tor of azo dye in TWW (Li et al. 2015). Additionally, two other peaks at around Ex/Em = 300–315 nm/380–382 nm Fluorescence data of wastewater as well as treated wastewater indicate the protein-like materials and the peak at around are thought to well correlate with other parameters including Ex/Em = 270–295 nm/350–362 nm indicates fulvic acid. biochemical oxygen demand (BOD), chemical oxygen demand The synergistic effect of Fe O NPs-induced solar irradia- (COD) and total organic carbon (TOC) (Reynolds 2002). In 2 3 tion caused a redshift in excitation emission wavelength addition, removal of dyes also reduces BOD, COD and TOC of all organic matters and the fluorescence intensity also of wastewater. Hence, to validate the degradation of DOM of decreased (Table  1). The resulting redshift could be due TWW under solar irradiation in the presence of Fe O NPs, 2 3 to the destruction of various fluorophores (all absorbing we also measure the environmentally important parameters at long wavelength) via indirect photochemistry excited at (BOD , COD and TOC) of TWW. Table 2 represents the per- long wavelength. In addition, destruction of fluorophores cent removal of TOC, COD and BOD of TWW after catalyst- by direct photochemistry excited at both wavelength or by induced solar irradiation (40 h). The BOD, COD and TOC of Fig. 7 A representative illustration of the three-dimensional excitation emission matrix (3DEEM) fluorescence spectra of PB dye solution. a Raw solution, b at 20 h of irradiation in the presence of Fe O NPs 2 3 1 3 73 Page 8 of 11 Applied Water Science (2018) 8:73 Fig. 8 A representative illustration of three-dimensional excitation emission matrix (3DEEM) fluorescence spectra of wastewater. a Raw waste- water, b at 40 h of irradiation in the presence of Fe O NPs 2 3 Table 1 Fluorescence properties Samples Peak intensities with coordinates (excitation/emission wavelengths) of Procion blue dye and textile wastewater Peak 1 Peak 2 Peak 3 Procion blue dye solution  Raw 0.06 (375 nm/460 nm) 0.07 (365 nm/452 nm) 0.02 (295 nm/354 nm)  Fe O induced 0.007 (380 nm/432 nm) 0.01 (340 nm/434 nm) 0.01 (280 nm/308 nm) 2 3 solar irradiated for 20 h days Textile wastewater  Raw 0.01 (390 nm/442 nm) 0.01 (300 nm/380 nm) 0.01 (270 nm/350 nm)  Fe O induced 0.008 (440 nm/508 nm) 0.009 (315 nm/382 nm) 0.01 (295 nm/362 nm) 2 3 solar irradiated for 40 h Table 2 Reduction in TOC, COD and BOD of real textile wastewater TWW are 208, 409 and 89 mg/L, respectively. Data in Table 2 after the treatment process (40 h) indicates that all those properties were improved after 40 h of solar irradiation with catalyst Fe O NPs. After 40 h of pho- BOD (%) COD (%) TOC (%) 2 3 tocatalytic irradiation, TOC, COD and BOD were reduced by After catalyst-induced solar irradia- 37.89 44.68 42.2 42.2, 44.68 and 37.89%, respectively. By the influence of solar tion days irradiation in the presence of Fe O NPs, complex organic 2 3 compounds are converted to simple compounds such as carbon dioxide, water, nitrate, amide and carboxylic acids (Hussein and Abbas 2010; Xu et al. 2012) and consequently the BOD, COD load and TOC of TWW are decreased. This result again 1 3 Applied Water Science (2018) 8:73 Page 9 of 11 73 proves the degradation of DOM from TWW using Fe O NPs 2 3 under solar irradiation. However, the improvement rate is less in comparison to some other treatment, i.e., at 10 kGy direct gamma irradiation, the BOD and COD of TWW reduced by 59 and 61%, respectively (Parvin et al. 2015). These rates of reduction (Table 2) suggest that degradation compounds, especially low molecular weight aldehydes and organic acids, still remain in solution. So, it is recommended that, to achieve complete mineralization, a little higher concentration of Fe O 2 3 NPs in wastewater is necessary. Eec ff t of degraded wastewater on plant growth Textile wastewaters are thought to hinder plant growth (Parvin et al. 2015), as the water quality is worse compared to the standard for use for irrigation purpose. Hence, the treated wastewater was irrigated to plants to compare the effect of treated wastewater on plant growth with raw waste- water. Figure 9 represents the morphological parameter of Malabar spinach nourished by water (control), TWW and catalyst-induced solar-irradiated TWW (TWW1), respec- tively. The morphological data (e.g., plant height, number of leaves, root length and dry mass) given in Fig. 9 were meas- ured after 45 days as shown. As expected, plants irrigated by TWW showed very low morphological properties in comparison with plants treated with normal water, because wastewaters having low DO, higher concentration of DOM and BOD load hinder plant growth. However, when we nour- ish the plants with catalyst-induced solar-irradiated waste- water, the value of plant growth becomes higher, though Fig. 9 Morphological properties of Malabar spinach after irrigation with water (control), wastewater (TWW) and catalyst-induced irradi- these values of plant morphology are still less in compari- ated wastewater (TWW1) son to the values of the control. However, in our previous work (Parvin et al. 2015), we decolorized TWW, using ion- linearly increased with time and the best results were izing gamma irradiation, which showed a fertilizing effect on plant growth. The possible explanation is solar radiation found at 40  h of solar irradiation for TWW. As for Pb dye solution of 50 mg/L concentration, the rate of deg- is not so intense like the most penetrating ionizing gamma irradiation to break the azo dye completely into nitrogen radation (80%) reached in equilibrium within 20 h using 5 mg/l Fe O NPs. The degradation of fluorescent DOM and ammonia, which is the reason for suppressing the plant 2 3 growth (though little), instead of acting as a fertilizer. How- of textile wastewater and dye solution by means of fluores- cence intensity can be described well by the second-order ever, using solar radiation is cost-effective and renewable compared to gamma radiation, as gamma radiation plants kinetic model. Analysis of 3DEEM revealed that, after photocatalytic irradiation, the intensity of humic acid is require high maintenance cost and the source Co is not renewable. Hence, the use of a relatively high concentration reduced, which is the main florescence indicator of azo dye in TWW. The degradation of DOM is again supported by of Fe O NPs (more than 5 mg/l) to accelerate the degrada- 2 3 tion ability of solar radiation is recommended in degrading the reduction of BOD, COD and TOC of TWW, indicating the applicability of this method (use of nanocatalyst under the dye and DOM completely. sunlight) in open lagoon/pond of the textile wastewater treatment plant. The catalyst-induced solar-irradiated Conclusions wastewater is found to have less effect on plant growth compared to raw wastewater. However, a little higher con- We synthesized properly Fe O NPs and it has also been centration of Fe O NPs is recommended for the complete 2 3 2 3 degradation of DOM. Hence, in our next work, we will proved by UV–Vis, FTIR spectra and SEM images analy- sis. Degradation of DOM of the dye solution and TWW focus on catalyst Fe O NPs concentration-dependent dye 2 3 1 3 73 Page 10 of 11 Applied Water Science (2018) 8:73 Khataee AR, Kasiri MB (2010) Photocatalytic degradation of organic and the DOM degradation of synthetic dye solution and dyes in the presence of nanostructured titanium dioxide: Influ- TWW. ence of the chemical structure of dyes. J Mol Catal A Chem 328(1–2):8–26. https ://doi.org/10.1016/j.molca ta.2010.05.023 Open Access This article is distributed under the terms of the Crea- Li WT, Xu ZX, Wu Q, Li Y, Shuang CD, Li AM (2015) Characteri- tive Commons Attribution 4.0 International License (http://creat iveco zation of fluorescent dissolved organic matter and identification mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- of specific fluorophores in textile effluents. 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Applied Water ScienceSpringer Journals

Published: May 4, 2018

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