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Abstract
resources Article Visible Light-Driven Photocatalytic Degradation of Ciprofloxacin, Ampicillin and Erythromycin by Zinc Ferrite Immobilized on Chitosan 1 2 , 1 , 3 Nehad Ahmed Hassan Mohamed , Rehab Nabil Shamma * , Sherien Elagroudy 4 , 5 , and Adewale Adewuyi * Public Works Department, Faculty of Engineering, Ain Shams University, Cairo 11535, Egypt Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, Cairo University, Cairo 11561, Egypt Egypt Solid Waste Management Center of Excellence, Ain Shams University, Cairo 11535, Egypt Department of Chemical Sciences, Faculty of Natural Sciences, Redeemer ’s University, Ede 230, Osun State, Nigeria Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK * Correspondence: rehab.shamma@pharma.cu.edu.eg (R.N.S.); walexy62@yahoo.com (A.A.); Tel.: +20-111-930-1245 (R.N.S.); +2348035826679 (A.A.) Abstract: This study investigated the synthesis of zinc ferrite immobilized on chitosan (ZnFe O @Chitosan) 2 4 and its application in the photodegradation of ciprofloxacin (CIP), ampicillin (AMP) and erythromycin (ERY) in aqueous solution. Results from Fourier transform infrared spectroscopy (FTIR) revealed peaks suggesting its synthesis, while signals from X-ray diffraction (XRD) showed diffraction patterns confirming the synthesis of ZnFe O @Chitosan with a crystallite size of 35.14 nm. Scanning electron 2 4 2 1 microscopy (SEM) revealed a homogeneous morphology with a surface area of 12.96 m g from the Brunauer–Emmett–Teller (BET) analysis. The vibrating sample magnetometry (VSM) result revealed Citation: Hassan Mohamed, N.A.; a saturation magnetization of 2.38 emu g . The photodegradation study of CIP, AMP and ERY Shamma, R.N.; Elagroudy, S.; showed that both photodegradation and adsorption were taking place at the same time with the Adewuyi, A. Visible Light-Driven Photocatalytic Degradation of percentage degradation efficiency in the order CIP (99.80 0.20%) > AMP (94.50 0.10%) > ERY Ciprofloxacin, Ampicillin and (83.20 0.20%). ZnFe O @Chitosan exhibited high stability with capacity > 90% even at the 15th 2 4 Erythromycin by Zinc Ferrite regeneration cycle, suggesting a viable economic value of ZnFe O @Chitosan. 2 4 Immobilized on Chitosan. Resources 2022, 11, 81. https://doi.org/ Keywords: adsorption; antibiotics; catalysis; ferrite; photodegradation 10.3390/resources11100081 Academic Editor: Eveliina Repo Received: 21 August 2022 1. Introduction Accepted: 16 September 2022 Contamination of natural sources of drinking water by antibiotics is a global con- Published: 22 September 2022 cern [1]. The contamination is on the rise because of the unregulated use of antibiotics Publisher’s Note: MDPI stays neutral in some nations of the world [2]. The ease of purchasing antibiotics without medical with regard to jurisdictional claims in prescription in some countries has encouraged self-medication, resulting in the excessive published maps and institutional affil- use of antibiotics. The excessive use of antibiotics is one of the causes of their presence iations. in environmental natural water-like surface and underground water systems. These an- tibiotics may become persistent in the environment or may decompose to form products that are toxic to humans and the environment. Some of the decomposition products can cause serious health challenges like cancer. Apart from this, the presence of antibiotics in Copyright: © 2022 by the authors. the environmental natural water system has led to far more serious consequences like the Licensee MDPI, Basel, Switzerland. emergence of drug-resistant strains of pathogenic organisms [3], which, in turn, hampered This article is an open access article the efficacies of well-known antibiotics. Unfortunately, previously efficient antibiotics are distributed under the terms and now losing efficacy. It is important that these antibiotics are removed from water in order conditions of the Creative Commons to avoid the challenges associated with their presence in natural sources of drinking water. Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ Many antibiotics have been detected in water [4,5], including ciprofloxacin (CIP), 4.0/). ampicillin (AMP) and erythromycin (ERY) reported in surface water as contaminants [6–9]. Resources 2022, 11, 81. https://doi.org/10.3390/resources11100081 https://www.mdpi.com/journal/resources Resources 2022, 11, 81 2 of 17 Their presence in water is of serious concern, although efforts have been made to remove them from water, but most of these efforts have shortcomings, like incomplete removal or being expensive. It is important to develop a process that can overcome such shortcomings with an affordable and sustainable approach. Photocatalysis is a green approach which has shown exceptional performance in the degradation of organic pollutants in water [10–12]. Photocatalysis has the potential of overcoming these shortcomings with the capacity for complete degradation of antibiotics in water [13]. Zinc oxide (ZnO) is an example of a photocatalyst that can be used in photocatalysis for the photocatalytic degradation of antibiotics. Unfortunately, ZnO is limited in its photocatalytic application, because it is photoactive in UV light due to its large bandgap energy. Previous studies have reported the use of ZnO particles for the degradation of amoxi- cillin, CIP, AMP and cloxacillin under UV light irradiation in aqueous solutions [14]. The study revealed a degradation efficiency of approximately 50% for CIP, creating the need for improvement. ZnO is active under UV light irradiation, which increases the process cost since there is a need to get a UV light source, unlike in the case of materials which are visible-light sensitive. A similar observation was also recorded recently using ZnO- functionalized fly-ash-based zeolite for the degradation of CIP which exhibited complete degradation [15]; despite the complete degradation, provision of UV light sources is an additional cost which eventually increases process cost. Developing ZnO into materials that are visible-light sensitive will go a long way in helping to reduce process cost. One of the ways of achieving this will be to incorporate ZnO into other particles, which reduces its bandgap energy. A good example of this is zinc ferrite (ZnFe O ). Ferrites are useful in this 2 4 regard because of their relatively narrow bandgap of approximately 2.0 eV, which makes it suitable for photocatalysis in the visible-light region. Spinel ferrites were recently reported for the degradation of tetracycline hydrochlo- ride [16]. Moreover, magnesium ferrite (MgFe O ) and manganese ferrite (Mn Fe O ) 2 4 x 3-x 4 have shown similar capacities against tetracycline [17] and sulfamethoxazole [18], respec- tively. Furthermore, high performance has been reported from the synergistic activity of MnFe O and molybdenum disulfide (MoS) for the degradation of tetracycline [19]. 2 4 Photocatalytic degradation of antibiotics by ferrite has proved to be a good solution for the treatment of antibiotic-contaminated water due to its soft magnetic properties, high catalytic activities and ease of recycling through magnetic separation [20]. However, a recent study revealed that the performance of a photocatalyst can be enhanced via a simple modification process. The current study proposes the modification of ZnFe O by organic molecule such 2 4 as chitosan. The use of chitosan will help stabilize the particles of ZnFe O by reducing 2 4 aggregation and helping to promote the recovery of ZnFe O particles from solution. A 2 4 previous study has shown that the efficiency of modified photocatalysts may be attributed to high light absorption, formation of step scheme heterojunction and interfacial charge sep- aration. Being a polysaccharide, chitosan contains random distribution of -(1–4)-linked D-glucosamine and N-acetyl-D-glucosamine. It is either neutral or negatively charged in acidic medium, which allows it to form electrostatic complexes or multilayer structure. Its nontoxicity, biocompatibility and biodegradability make it suitable for various applications such as in water treatment. This study aimed at investigating the preparation of ZnFe O via coprecipitation and 2 4 its immobilization on chitosan to further improve on its separation from aqueous solution when used as a photocatalyst for the photodegradation of antibiotics. ZnFe O @Chitosan 2 4 was proposed as a photocatalyst for the degradation of CIP, AMP and ERY in aqueous solution. Therefore, this study was aimed at the photodegradation of CIP, AMP and ERY under visible-light irradiation using ZnFe O @Chitosan. 2 4 2. Materials and Methods 2.1. Materials Zinc chloride hexahydrate (ZnCl .6H O), ferric chloride hexahydrate (FeCl .6H O), 2 2 3 2 chitosan, acetic acid, NaOH, C H OH, HCl, oleic acid, ciprofloxacin (CIP), ampicillin 2 5 Resources 2022, 11, 81 3 of 17 (AMP), erythromycin (ERY), isopropyl alcohol (IPA), ammonium oxalate (AO), chloro- form (CH), and all other chemicals used were purchased from the Aldrich Chemical Co., Gillingham, UK. 2.2. Synthesis of ZnFe O Particles 2 4 To prepare ZnFe O particles, mixtures of FeCl .6H O (0.4 M) and ZnCl .6H O (0.2M) 2 4 3 2 2 2 were continuously stirred for 60 min, after which oleic acid (15 mL) was added as a capping agent. The mixture was maintained at a temperature of 80 C and a pH range of 10–12 by dropwise addition of NaOH (2 M) until the appearance of precipitate while stirring for 2 h. The mixture was cooled to room temperature, filtered, and washed severally with water and ethanol. The residue obtained was oven-dried at 105 C for 12 h and transferred to the furnace at 550 C for 18 h. 2.3. Synthesis of ZnFe O @Chitosan Particles 2 4 To prepare ZnFe O @Chitosan, chitosan (1 g) was dissolved in acetic acid (50 mL, 2 4 2% v/v) and sonicated for 60 min. ZnFe O (2 g) was added to the solution and stirred 2 4 for 60 min. While maintaining room temperature, 30 mL of NaOH (1 M) were added and stirred for 40 min to form precipitates. The ZnFe O @Chitosan formed was filtered and 2 4 washed severally with deionized water. The residue obtained was oven-dried at 40 C for 12 h. 2.4. Characterization of ZnFe O @Chitosan Particles 2 4 The functional groups in ZnFe O @Chitosan were determined using FTIR (Agilent 2 4 Technologies); spectrum was recorded in the range of 400–4500 cm . The BET surface area was determined by N gas adsorption using Nova 3200 quanta chrome. TG analysis was carried out using a Mettler thermogravimetric analyzer (SDT Q600 V20.9 Build 20). The X-ray diffraction pattern was measured in 2 ranging from 5 to 90 using an X-ray diffractometer (Philip XRD-1390 PW model) with filtered Cu K radiation operated at 40 kV and 40 mA. The SEM image was recorded using SEM JSM-T25 (JOEL Co., Japan), while elemental composition was estimated on EDS. VSM was carried out on a magnetometer and UV-visible absorption spectra were recorded on a UV-visible spectrophotometer (UV-vis: Cary 60). 2.5. Photocatalytic Degradation of CIP, AMP and ERY by ZnFe O @Chitosan 2 4 The photodegradation study was carried out under visible light using a low-cost solar simulator (LSO1O6, 150 W Xe light source) with a filter holder and 90 beam turner. The degradation was achieved by contacting 100 mL of either CIP, AMP or ERY at a concentration of 5.00 mg L with 0.1 g of ZnFe O @Chitosan particle in a 150 mL beaker 2 4 for 180 min while stirring gently at 80 rpm under the simulated visible-light irradiation, ensuring a distance of 20 cm between the UV lamp and the test solution. Samples were withdrawn at different intervals to monitor the degradation rate. The concentrations of CIP ( = 271 nm), AMP ( = 420 nm) and ERY ( = 285 nm) were measured max max max using a UV-visible spectrophotometer (Perkin Elmer, Lambda 750 spectrometer). The effect of the ZnFe O @Chitosan weight on degradation was checked by varying the weight of 2 4 ZnFe O @Chitosan from 0.1 to 0.5 g, while the effect of concentration of CIP, AMP or 2 4 ERY on degradation capacity was evaluated by varying the concentration from 1.00 to 5.00 mg L (CIP, AMP or ERY), and the effect of pH was determined by varying the pH solution from 2 to 10. The experiment was repeated in the dark to establish the adsorption– desorption equilibrium. All the experiments were repeated three times and values were presented as mean value. The degradation efficiency was calculated as: Degradation E f f iciency (%) = 100 x (1 ) (1) o Resources 2022, 11, 81 4 of 17 where C is the initial concentration of CIP, AMP or ERY, and C is the concentration of CIP, o t AMP or ERY at time t. The adsorption capacity (q ) and the percentage removal (% removal) for the adsorption–desorption equilibrium experiment in the dark was calculated as: C C V ( ) o t q = (2) (C Ct) % removal = X 100 (3) Co Equation (4) was obtained by combining Equations (2) and (3) (% removal X C X V) q = (4) 100 X m 1 1 where C (mg L ) is the initial concentration of CIP, AMP or ERY, C (mg L ) is the o t concentration of CIP, AMP or ERY at time t; m is the weight (g) of ZnFe O @Chitosan used, 2 4 V represents the volume in litres (L) and q (mg g ) is the adsorption capacity. 2.6. Evaluation of Reactive Oxygen Species Scavenging Capacity In order to understand the mechanism of operation of ZnFe O @Chitosan, the role of 2 4 reactive oxygen species (ROS) in the photodegradation of CIP, AMP and ERY was inves- tigated using isopropyl alcohol (IPA) as a hydroxyl radical (OH) scavenger, ammonium oxalate (AO) as a scavenger for hole (h ) and the scavenger for superoxide ion radical (O ) being chloroform (CH). The scavengers were separately introduced into the photodegrada- tion process as a concentration of 1 mM. The process conditions (ZnFe O @Chitosan weight, 2 4 concentration of CIP, AMP or ERY, photodegradation time, and pH) for photodegradation with and without scavengers was kept constant. 2.7. Re-Useability and Stability of ZnFe O @Chitosan 2 4 To determine re-useability, the ZnFe O @Chitosan was recovered after the degrada- 2 4 tion time, washed with solvents (deionized water, 0.1 M HCl, ethanol or a mixture of ethanol and 0.1 M HCl (3:2)) and dried in the oven at 80 C for 5 h before it was reused for the photodegradation process. The treated aqueous solution was analyzed to check for the leaching of ZnFe O into solution using inductively coupled plasma–optical emission 2 4 spectroscopy (ICP–OES). The ICP–OES analysis was carried out at the end of each treat- ment cycle with ZnFe O @Chitosan. The photostability of the ZnFe O @Chitosan for the 2 4 2 4 photodegradation of CIP, AMP and ERY was evaluated in fifteen (15) successive cycles of operation. 3. Results and Discussion 3.1. Synthesis and Characterization of ZnFe O @Chitosan 2 4 The FTIR spectrum of ZnFe O @Chitosan revealed the functional groups it contained, 2 4 as shown in Figure 1a. The spectrum revealed a peak at 3420 cm , which was attributed to the O-H stretching, while the peak at 2892 cm was assigned to the C-H stretching of alkane. The -NH C stretch was observed at 2352 cm , while the signal corresponding to the C=O carbonyl stretch of amide was seen at 1612 cm . The N-H and C-H bending 1 1 appeared at 1584 and 1580 cm , respectively. The peak at 1432 cm was assigned to C-O stretch, while the anti-asymmetric stretching vibration of C-O-C appeared at 1027 cm . The signals appearing at 593 and 387 cm correspond to the stretching frequencies of Zn-O and Fe-O, respectively. The BET surface area of ZnFe O @Chitosan is shown in 2 4 2 1 Figure 1b, which revealed a surface area of 12.96 m g , total pore volume (at P/P = 0.900) 3 1 of 0.109 cm g and a mean pore diameter of 33.71 nm. The BET isotherm exhibited by ZnFe O @Chitosan is of type II, which suggests unrestricted monolayer–multilayer 2 4 adsorption that is common to mesoporous adsorbents [21]. The XRD diffraction (Figure 1c) showed the most intense peak at 2 = 35.61 with a plane spacing corresponding to Resources 2022, 11, 81 5 of 17 (311), which is the plane previously reported for ZnFe O particles [22] with other planes 2 4 corresponding to (110), (111), (134), (220), (222), (400), (422), (511), (440), (620), (533), (444), (642), (731) and (800), as seen in the pattern [22,23]. Equation (5) shows an expression from which the crystallite size of ZnFe O @Chitosan may be calculated considering its X-ray 2 4 line broadening from the reflections of (311) and Debye–Scherrer ’s formula [24]: Kl Resources 2022, 11, x FOR PEER REVIEW D = 6 of 19(5) b Cosq Figure 1. FTIR (a), BET (b), XRD (c) and TGA analysis (d) of ZnFe2O4@Chitosan. Figure 1. FTIR (a), BET (b), XRD (c) and TGA analysis (d) of ZnFe O @Chitosan. 2 4 The SEM micrograph is presented in Figure 2a, revealing district packs of particles on the surface of ZnFe2O4@Chitosan which may be seen to be homogeneous. The EDS result (Figure 2b) confirms the presence of carbon (c), oxygen (O), nitrogen (N), iron (Fe) and zinc (Zn) in the molecule of ZnFe2O4@Chitosan, while elemental surface mapping is shown in Figure 2c (C1–5). Resources Resources 2022 2022 , 11 , 11 , x FO , x FO R P R P EER EER R R E E VIEW VIEW 5 of 5 of 19 19 Resources 2022, 11, x FOR PEER REVIEW 5 of 19 −− 11 1b, which revealed a surface area of 12.96 m² g , total pore volume (at P/Po = 0.900) of 1b, which revealed a surface area of 12.96 m² g , total pore volume (at P/Po = 0.900) of −− 11 0. 0.10 109 cm 9 cm³³gg and and a me a mean an pore diame pore diametteerr of of 33.71 n 33.71 nm m. The BET . The BET iso isottherm exh herm exhiibited by bited by −1 1b, which revealed a surface area of 12.96 m² g , total pore volume (at P/Po = 0.900) of ZnFe ZnFe 22 O O 44@Chitosan is o @Chitosan is off type II, which type II, which suggests suggests uunnre ressttri rict cteedd monol monolaaye yer– r–mu multi ltillaayyeerr a add-- −1 0.109 cm³g and a mean pore diameter of 33.71 nm. The BET isotherm exhibited by sorp sorpttiion th on that at is com is comm mo on to n to m meesop sopo orous rous adsorb adsorben ents ts [2 [21] 1]. The X . The XR RD D dif difffrraact ction (F ion (Fiig gure ure 1c) 1c) ZnFe2O4@Chitosan is of type II, which suggests unrestricted monolayer–multilayer ad- showed the showed the most most in in tense tense peak peak at at 22θθ = 35 = 35 .6 .6 1° 1° wi wi tt h h a a p p ll aa n n e e sp sp aa cc ii n n g correspondi g correspondi ng t ng t o o ( ( 311 311 ), ), sorption that is common to mesoporous adsorbents [21]. The XRD diffraction (Figure 1c) which which is t is t h h e e pla pla n n e previously report e previously report ed for ZnFe ed for ZnFe 22 O O 44 particle particle s [22] with s [22] with oth oth ee r r p p ll anes anes corre corre -- showed the most intense peak at 2θ = 35.61° with a plane spacing corresponding to (311), sponding to (110), (111), (134), (220), (222), (400), (422), (511), (440), (620), (533), (444), (642), sponding to (110), (111), (134), (220), (222), (400), (422), (511), (440), (620), (533), (444), (642), which is the plane previously reported for ZnFe2O4 particles [22] with other planes corre- ((731 731)) aannd d (8 (800 00), as seen ), as seen iinn t thhe p e paattttern [2 ern [22, 2,2233]]. E . Eqquuaatition (5 on (5) ) shows shows an expr an express essiioonn from from sponding to (110), (111), (134), (220), (222), (400), (422), (511), (440), (620), (533), (444), (642), whi whicch t h thhe crysta e crystallllit ite siz e sizee of of ZnFe ZnFe 22 O O 44@ @C Chitosan m hitosan maay be c y be caalc lculated considerin ulated considering its X g its X--ray ray (731) and (800), as seen in the pattern [22,23]. Equation (5) shows an expression from line broadening from line broadening from the reflec the reflec tions o tions o ff (311) (311) and Deb and Deb y y e–Scherre e–Scherre r’s formula [24]: r’s formula [24]: which the crystallite size of ZnFe2O4@Chitosan may be calculated considering its X-ray Resources 2022, 11, 81 6 of 17 𝐾𝜆 𝐾𝜆 line broadening from the reflections of (311) and Debye–Scherrer’s formula [24]: (5 (5 )) 𝐷= 𝐷= 𝛽 𝛽 𝑜𝜃𝐶𝑠 𝑜𝜃𝐶𝑠 𝐾𝜆 (5) 𝐷= From Equation (5), D is the average crystallite size of ZnFe O @Chitosan, K represents From Equation (5), D is the average crystallite size of ZnFe2O 2 4@Chito 4 san, K represents From Equation (5), D is the average crystallite size of ZnFe2O4@Chitosan, K represents 𝛽 𝑜𝜃𝐶𝑠 a constant taken as 0.89. l is the X-ray wavelength (1.5406 Å), while and are the full aa cco ons nsta tant nt tak takeen n a ass 0. 0.89 89. . λλ is is the the X-r X-raay y wavelen waveleng gth th ( (11.5 .5440066 Å) Å), wh , while ile ββ and and θθ ar are e th the full e full From Equation (5), D is the average crystallite size of ZnFe2O4@Chitosan, K represents width of diffraction line at half of the maximum intensity (FWHM) and Bragg’s angle (at width width of diffr of diffr action line at ha action line at half of the lf of the m m aaxim xim u um in m inte tensity nsity (FW (FWH HM M)) an and Br d Bragg’ agg’ s s angle (at angle (at a constant taken as 0.89. λ is the X-r peak ay wavelen (311)), r gespectively th (1.5406 Å) [25 , wh ]. The ile β and crystallite θ are size the full for ZnFe O @Chitosan was found to 2 4 p peeak ak ( (3311 11)) )), , rreesp spect ectiiv veelly y [2 [25] 5]. The . The cr crys ysta talli llite te s siize ze for for Z Zn nFe Fe 22 O O 44@Chitosan @Chitosan w waas fo s found to und to be be width of diffraction line at half of the be m 35.14 axim nm. um in The tensity crystallite (FWHsize M) an isd Br important agg’s angle (at in understanding its diffusion properties. 35 35.1 .14 nm 4 nm. . Th The crys e crysttaalllliitte s e siize ze is is import importaan nt in t in unde unders rsttaandin nding i g ittss di diffffus usion proper ion propertie tiess. . Ap- Ap- Apparently, this can be expressed as [26,27]: peak (311)), respectively [25]. The crystallite size for ZnFe2O4@Chitosan was found to be parently, this can be expressed as [26,27]: parently, this can be expressed as [26,27]: 35.14 nm. The crystallite size is important in understanding its diffusion properties. Ap- 2 2 22 22 Ʈ Ʈ = r = r = r ᴫᴫD ( D ( D 66 (6))) parently, this can be expressed as [26,27]: where where Ʈ Ʈ i iss th the av e aveerraag ge e di diff ffusion usion tim timee of of charge charge c caarri rrier ers f s frrom om b bu ulk lk s so olu lution tion to to the the su surf rface ace 2 2 where Ʈ = r is the ᴫD ( average diffusion time of charge carriers6) from bulk solution to the surface of of ZnFe of ZnFe 22 O O 44 @ @ C C hitosan, hitosan, and and D represen D represen ts ts the d the d ii ffusion ffusion coefficien coefficien t o t o ff the ch the ch arge arge s. s. Accordin Accordin g g ZnFe O @Chitosan, and D represents the diffusion coefficient of the charges. According to 2 4 where Ʈ is the average diffusion time of charge carriers from bulk solution to the surface to the expression (Equation (6)), the larger the size of a catalyst, the longer the diffusion to the expression (Equation (6)), the larger the size of a catalyst, the longer the diffusion the expression (Equation (6)), the larger the size of a catalyst, the longer the diffusion time, of ZnFe2O4@Chitosan, and D represents the diffusion coefficient of the charges. According tim timee, wh , which ich m meeans ans th the m e moore s re su uscep sceptib tiblle e it it is is to to agg aggrrega egattion ion (rec (recombinat ombinatiion on eeffec ffectt)). Such . Such which means the more susceptible it is to aggregation (recombination effect). Such recombi- to the expression (Equation (6)), the larger the size of a catalyst, the longer the diffusion recom recomb bina inattio ion le n leads ads to to de decreas creaseed c d caattaally ytic tic p prrop oper erty ty [2 [27, 7,2288]. ]. It It is is i im mp po ortan rtant t th thaatt the cr the crys ys-- nation leads to decreased catalytic property [27,28]. It is important that the crystallite size time, which means the more susceptible it is to aggregation (recombination effect). Such ta tallllitite e si size ze i iss smal small.l. The The cr cryst ystaalllliittee s siize ze of ZnF of ZnFee 22 O O 44@ @C Chitos hitosaann f faallllss w wiith thing ing the the r raange nge of of is small. The crystallite size of ZnFe O @Chitosan falls withing the range of previously 2 4 recombination leads to decreased catalytic property [27,28]. It is important that the crys- p prrev evious iously ly rreep po orted rted ssiizes ( zes (37 to 4 37 to 455 nm nm) for ) for sp spin inel ferr el ferrite [ ite [2299]], sug , sugg geest sting a ing a good good cat cataalys lystt reported sizes (37 to 45 nm) for spinel ferrite [29], suggesting a good catalyst functional tallite size is small. The crystallite size of ZnFe2O4@Chitosan falls withing the range of func func tion tion al al s s ii zz ee for for ZnFe ZnFe 22 O O 44 @Chito @Chito san san . . size for ZnFe O @Chitosan. 2 4 previously reported sizes (37 to 45 nm) for spinel ferrite [29], suggesting a good catalyst The thermal degradation is shown in Figure 1d, which showed three major losses. The thermal degradation is shown in Figure 1d, which showed three major losses. The thermal degradation is shown in Figure 1d, which showed three major losses. The functional size for ZnFe2O4@Chitosan. The firs The first t loss loss at r at raang nge 0 e 0––118800 °C °C i iss ab abou out t 5. 5.58% 58%, which , which was was at attrib tribut uted to ed to a los a losss o off v voola lattile ile first loss at range 0–180 C is about 5.58%, which was attributed to a loss of volatile and The thermal degradation is shown in Figure 1d, which showed three major losses. and and adso adsorb rbed ed wa water m ter mo olec lecu ule les. Th s. This is is is ffo ollowed llowed b by y a a second m second maajor jor los losss a att ran rang gee 2 21100––415 415 adsorbed water molecules. This is followed by a second major loss at range 210–415 C, The first loss at range 0–180 °C is about 5.58%, which was attributed to a loss of volatile °C, wh °C, wh ich ich is is 11 77 .41% .41% of of tot tot aa ll mas mas ss and and wa wa s s at at trib trib ut ut ed ed tt o o the the decomp decomp osi osi tt ion ion of of the the chito chito ss an an which is 17.41% of total mass and was attributed to the decomposition of the chitosan and adsorbed water molecules. This is followed by a second major loss at range 210–415 str stru ucture w cture wiith loss o th loss off H H 22O, O, N NH H 33, CO , CO, CO , CO 22 and C and CH H 33C COOH, which OOH, which was considered to be was considered to be structure with loss of H O, NH , CO, CO and CH COOH, which was considered to be 2 3 2 3 °C, which is 17.41% of total mass and was attributed to the decomposition of the chitosan pyrrolic degradation of chitosan as previously reported [30,31]. Moreover, previous study ppyrr yrroli olic c degr degradation adation of ch of chitosan itosan aas s ppr rev eviou iouslsly y rep reported orted [3 [0, 30 3,1 31 ]. ]. Mor Mor eov eover er, p , pr rev evious ious ststudy udy structure with loss of H2O, NH3, CO, CO2 and CH3COOH, which was considered to be has has shown shown th that at the the degr degrad adat ation o ion off chi chitto ossan an can can ta take ke p pllace ace b by y ran rand dom om b brrea eaking king of of the the C C-- has shown that the degradation of chitosan can take place by random breaking of the pyrrolic degradation of chitosan as previously reported [30,31]. Moreover, previous study 1 −− 11 O- O- C C skel skel eta eta ll bond bond [30 [30 –33 –33 ]] , ,whi whi cc h h wa wa s s seen seen ii n n t t h h e FTIR e FTIR result result ( ( F F ii g g ure 1 ure 1 a a )) at at 10 10 27 cm 27 cm . The . The C-O-C skeletal bond [30–33], which was seen in the FTIR result (Figure 1a) at 1027 cm . has shown that the degradation of chitosan can take place by random breaking of the C- thir thir The d im d im thir p po d ort rt important aan nt los t losss in in loss the the range in range the 4 range 41155––1100 415–1000 00 00 °C °C acco accoun C unts fo accounts ts for 2 r 266.3 .3 for 0% 0% 26.30% loss o loss off the the lossto to of ttaal m the l maa total ss ss, , −1 O-C skeletal bond [30–33], which was seen in the FTIR result (Figure 1a) at 1027 cm . The which ma which ma mass, which y b y bee may a attr ttribu be ibu attributed tted ed ttoo loss loss to of C of C lossH H of 44 th th CH at w at w that aass co was consider nsider consider ed ed to h to h ed to aavv have ee ta taken p ken p takenlla place acce v e viia via a a a a third important loss in the range 415–1000 °C accounts for 26.30% loss of the total mass, dehydrogenation mechanism as previously reported [30,34,35]. dehydrog dehydrog enation m enation m ee chan chan ism as pr ism as pr evio evio usly repor usly repor tt ed ed [30,34,35]. [30,34,35]. which may be attributed to loss of CH4 that was considered to have taken place via a The SEM micrograph is presented in Figure 2a, revealing district packs of particles on dehydrogenation mechanism as previously reported [30,34,35]. the surface of ZnFe O @Chitosan which may be seen to be homogeneous. The EDS result 2 4 (Figure 2b) confirms the presence of carbon (c), oxygen (O), nitrogen (N), iron (Fe) and zinc (Zn) in the molecule of ZnFe O @Chitosan, while elemental surface mapping is shown in 2 4 Figure 2c (C ). 1–5 The magnetic property of ZnFe O @Chitosan was investigated using vibration sample 2 4 magnetometry and the results are presented in Figure 2d with magnetic hysteresis loop, indicating that ZnFe O @Chitosan is magnetic. The saturation magnetization is found 2 4 to be 2.38 emu g , which is large enough for magnetic separation for practical applica- tions. Previous study has reported a high saturation magnetization [22,36,37] for ZnFe O ; 2 4 however, the observed low saturation magnetization in ZnFe O @Chitosan compared to 2 4 previous reports may be due to the immobilization of ZnFe O on chitosan, which may 2 4 have altered the inversion degree of ZnFe O . 2 4 The UV-visible spectrum is shown in Figure 3a, revealing absorbance in the visible region, which suggests that ZnFe O @Chitosan may have photocatalytic activity in the 2 4 visible-light region. The optical bandgap was determined from the Tauc plot method, as shown in Figure 3b; this was determined as described for a transition-type semiconductor (Equation (7): (µ hv) = A hv E (7) where hv is the frequency of incident light, A represents the proportionality constant, E is the bandgap and is the absorption coefficient. The bandgap for ZnFe O @Chitosan was 2 4 found to be 2.98 eV, which further corroborates the fact that ZnFe O @Chitosan may be 2 4 active for photodegradation within the visible-light region. Resources 2022, 11, 81 7 of 17 Resources 2022, 11, x FOR PEER REVIEW 7 of 19 Figure 2. SEM (a), EDS (b), surface mapping (c) and VSM analysis (d) of ZnFe2O4@Chitosan. Figure 2. SEM (a), EDS (b), surface mapping (c) and VSM analysis (d) of ZnFe O @Chitosan. 2 4 The magnetic property of ZnFe2O4@Chitosan was investigated using vibration sam- 3.2. Photodegradation Study ple magnetometry and the results are presented in Figure 2d with magnetic hysteresis The time-dependent degradation of CIP, AMP and ERY by ZnFe O @Chitosan at a 2 4 loop, indicating that ZnFe 21 O4@Chitosan is magnetic. The saturation magnetization is concentration of 5.00 mg L is presented in Figure 4a. The percentage degradation was −1 found to be 2.38 emu g , which is large enough for magnetic separation for practical ap- in the following order of efficiency: CIP (99.80 0.20%) > AMP (94.50 0.10%) > ERY plications. Previous study has reported a high saturation magnetization [22,36,37] for (83.20 0.20%). The photodegradation reached equilibrium after 150 min of treatment. ZnFe2O4; however, the observed low saturation magnetization in ZnFe2O4@Chitosan com- The degradation efficiency exhibited by ZnFe O @Chitosan towards the antibiotics might 2 4 pared to previous reports may be due to the immobilization of ZnFe2O4 on chitosan, which be molecular weight-dependent since the highest efficiency was found in CIP having the may have altered the inversion degree of ZnFe2O4. lowest molecular weight and the least efficiency found in ERY having the highest molecular The UV-visible spectrum is shown in Figure 3a, revealing absorbance in the visible weight. The molecular weight is in the increasing order of CIP (331.347 g mol ) < AMP 1 1 region, which suggests that ZnFe2O4@Chitosan may have photocatalytic activity in the (349.406 g mol ) < ERY (733.930 g mol ). The molecular structures of the antibiotics are visible-light region. The optical bandgap was determined from the Tauc plot method, as shown in Figure 3c–e; the lower the molecular weight, the higher the degradation efficiency shown in Figure 3b; this was determined as described for a transition-type semiconductor expressed by ZnFe O @Chitosan. The dark experiment revealed that adsorption was tak- 2 4 ing (Equation ( place at7the ): same time with the photocatalytic degradation. Therefore, the adsorption capacities as well as the percentage removal with time are presented in Figure 4b–d. The (∝ ℎ ) = (ℎ − ) (7) adsorption capacity and percentage removal increased with time and reached equilib- rium after 30 min of treatment. The adsorption capacity was 1.1 0.05 mg g in CIP, where hv is the frequency of incident light, A represents the proportionality constant, Eg 1 1 0.6 0.05 mg g in AMP, and 1.6 0.02 mg g in ERY, while the percentage removals is the bandgap and α is the absorption coefficient. The bandgap for ZnFe2O4@Chitosan were 22 0.05, 12 0.05 and 32 0.02% in CIP, AMP and ERY, respectively. The highest was found to be 2.98 eV, which further corroborates the fact that ZnFe2O4@Chitosan may adsorption capacity and percentage removal was expressed towards ERY. be active for photodegradation within the visible-light region. Resources 2022, 11, 81 8 of 17 Resources 2022, 11, x FOR PEER REVIEW 8 of 19 Figure 3. UV-visible absorbance spectra of ZnFe2O4@Chitosan (a), Tauc plot for ZnFe2O4@Chitosan Figure 3. UV-visible absorbance spectra of ZnFe O @Chitosan (a), Tauc plot for ZnFe O @Chitosan 2 4 2 4 (b), structure of CIP (c), structure of AMP (d) and structure of ERY (e). (b), structure of CIP (c), structure of AMP (d) and structure of ERY (e). 3.3. Effect of Operational Parameters 3.2. Photodegradation Study The effect of concentration (1.00 to 5.00 mg L ) on degradation efficiency and percent- The time-dependent degradation of CIP, AMP and ERY by ZnFe2O4@Chitosan at a −1 age removal (dark experiment) are presented in Figure 5a,b, respectively. The degradation concentration of 5.00 mg L is presented in Figure 4a. The percentage degradation was in efficiency increased as concentration reduced from 5.00 to 1.00 mg L , which may be due the following order of efficiency: CIP (99.80 ± 0.20%) > AMP (94.50 ± 0.10%) > ERY (83.20 to the reduction in the amount of antibiotic species to be degraded. As these species reduce, ± 0.20%). The photodegradation reached equilibrium after 150 min of treatment. The deg- ZnFe O @Chitosan had lesser work to execute, which resulted in an increase in efficiency. radatio 2 n 4 efficiency exhibited by ZnFe2O4@Chitosan towards the antibiotics might be mo- Moreover, when the concentration increases, more degradation products are produced lecular weight-dependent since the highest efficiency was found in CIP having the lowest that may occupy the active photodegradation site on ZnFe O @Chitosan. Therefore, since 2 4 molecular weight and the least efficiency found in ERY having the highest molecular adsorption has been confirmed to be taking place from the dark experiment conducted, −1 it weight. The molecular weight is in the increasing order of CIP (331.347 g mol ) < AMP becomes evident that, as adsorption takes place, there is the possibility of the photodegra- −1 −1 (349.406 g mol ) < ERY (733.930 g mol ). The molecular structures of the antibiotics are dation sites being populated with the adsorbed species as concentration increases, allowing shown in Figure 3c–e; the lower the molecular weight, the higher the degradation effi- more adsorbate to migrate to the photocatalysis sites on ZnFe O @Chitosan. This occur- 2 4 ciency expressed by ZnFe2O4@Chitosan. The dark experiment revealed that adsorption rence will reduce photon penetration or migration to the surface of ZnFe O @Chitosan 2 4 was taking place at the same time with the photocatalytic degradation. Therefore, the ad- to initiate photocatalytic activities. This incident is capable of reducing the formation of sorption capacities as well as the percentage removal with time are presented in Figure oxidants, which limits the interaction between generated holes and electrons in the conduc- 4b–d. The adsorption capacity and percentage removal increased with time and reached −1 equilibrium after 30 min of treatment. The adsorption capacity was 1.1 ± 0.05 mg g in Resources 2022, 11, 81 9 of 17 Resources 2022, 11, x FOR PEER REVIEW 9 of 19 tion band. However, contrary to this, the percentage removal increased with an increase in concentration of the antibiotics, which may be due to the fact that, as the concentration of −1 −1 CIP, 0.6 ± 0.05 mg g in AMP, and 1.6 ± 0.02 mg g in ERY, while the percentage removals antibiotics in solution increased, more species were available to interact with the surface of were 22 ± 0.05, 12 ± 0.05 and 32 ± 0.02% in CIP, AMP and ERY, respectively. The highest ZnFe O @Chitosan for adsorption. 2 4 adsorption capacity and percentage removal was expressed towards ERY. −1 Figure 4. (a) = Time-dependent degradation efficiency for CIP, AMP and ERY at 5.00 mg L , (b ) 1= Figure 4. (a) = Time-dependent degradation efficiency for CIP, AMP and ERY at 5.00 mg L , −1 Adsorption capacity and percentage removal for CIP at 5.00 mg L in the absence of visible light, (b) = Adsorption capacity and percentage removal for CIP at 5.00 mg L in the absence of visible −1 (c) = Adsorption capacity and percentage removal for AMP at 5.00 mg L in the absence of visible light, (c) = Adsorption capacity and percentage removal for AMP at 5.00 mg L in the absence of −1 light and (d) = Adsorption capacity and percentage removal for ERY at 5.00 mg L in the absence of visible light and (d) = Adsorption capacity and percentage removal for ERY at 5.00 mg L in the visible light. absence of visible light. 3.3. Effect of Operational Parameters −1 The effect of concentration (1.00 to 5.00 mg L ) on degradation efficiency and per- centage removal (dark experiment) are presented in Figure 5a,b, respectively. The Resources 2022, 11, 81 10 of 17 Resources 2022, 11, x FOR PEER REVIEW 11 of 19 Figure 5. (a) = Effect of concentration of CIP, AMP and ERY on the degradation efficiency of Figure 5. (a) = Effect of concentration of CIP, AMP and ERY on the degradation efficiency of ZnFe2O4@Chitosan, (b) = Effect of concentration of CIP, AMP and ERY on the percentage removal ZnFe O @Chitosan, (b) = Effect of concentration of CIP, AMP and ERY on the percentage re- 2 4 expressed by ZnFe2O4@Chitosan in the absence of visible light, (c) = Effect of weight of moval expressed by ZnFe O @Chitosan in the absence of visible light, (c) = Effect of weight of 2 4 −1 ZnFe2O4@Chitosan on degradation efficiency towards CIP, AMP and ERY at 5.00 mg L and (d) = ZnFe O @Chitosan on degradation efficiency towards CIP, AMP and ERY at 5.00 mg L and 2 4 Effect of weight of ZnFe2O4@Chitosan on percentage removal expressed towards CIP, AMP and (d) = Effect of weight −1 of ZnFe O @Chitosan on percentage removal expressed towards CIP, AMP and 2 4 ERY at 5.00 mg L in the absence of visible light. ERY at 5.00 mg L in the absence of visible light. ZnFe2O4@Chitosan expressed high degradation efficiency at low pH values but the The effect of weight of ZnFe O @Chitosan was also examined on the degradation 2 4 degradation efficiency decreased as the pH increases above 7 (Figure 6a,b). efficiency and the percentage removal, as shown in Figure 5c,d. It was observed in both cases that the performance of ZnFe O @Chitosan towards the degradation of CIP, AMP and 2 4 ERY increased as the weight of ZnFe O @Chitosan increased. This observation suggests 2 4 that, as the weight of ZnFe O @Chitosan increased, more active sites were available to 2 4 Resources 2022, 11, 81 11 of 17 initiate photodegradation and adsorption. Solution pH plays an important role in the photodegradation process. Resources 2022, 11, x FOR PEER REVIEW 12 of 19 ZnFe O @Chitosan expressed high degradation efficiency at low pH values but the 2 4 degradation efficiency decreased as the pH increases above 7 (Figure 6a,b). Figure 6. (a) = Effect of solution pH on the degradation efficiency of ZnFe2O4@Chitosan (0.1 g) Figure 6. (a) = Effect of solution pH on the degradation efficiency of ZnFe O @Chitosan (0.1 g) against 2 4 −1 against CIP, AMP and ERY at 5.00 mg L , (b) = Effect of solution pH on the percentage removal CIP, AMP and ERY at 5.00 mg L , (b) = Effect of solution pH on the percentage removal expressed −1 expressed by ZnFe2O4@Chitosan (0.1 g) towards CIP, AMP and ERY at 5.00 mg L , (c) = Plot of by ZnFe O @Chitosan (0.1 g) towards CIP, AMP and ERY at 5.00 mg L , (c) = Plot of 1nCo/Ct −1 2 4 1nCo/Ct versus irradiation time for CIP, AMP and ERY at 5.00 mg L and 0.1 g of ZnFe2O4@Chitosan versus irradiation time for CIP, AMP and ERY at 5.00 mg L and 0.1 g of ZnFe O @Chitosan and and (d) = Degradation efficiency of ZnFe2O4@Chitosan towards CIP, AMP and ERY 2 4 with and with- out (d) different ROS scaveng = Degradation efficiency ers.of ZnFe O @Chitosan towards CIP, AMP and ERY with and without 2 4 different ROS scavengers. The best pH for the photodegradation study is the acidic pH, which may be due to The best pH for the photodegradation + study is the acidic pH, which may be due to the fact that during low pH, more H ions are available that can react with water to form the fact that during low pH, more H ions are available that can react with water to form the hydroxyl radicals to promote the photodegradation process. On the other hand, the the hydroxyl radicals to promote the photodegradation process. On the other hand, the adsorption capacity was low at acidic pH (low pH value) but increased as the pH value adsorption capacity was low at acidic pH (low pH value) but increased as the pH value increased towards 7 (neutral pH value). Interestingly, the percentage removal dropped as increased towards 7 (neutral pH value). Interestingly, the percentage removal dropped as the pH value increased from 7 to 10. the pH value increased from 7 to 10. The photodegradation of CIP, AMP and ERY by ZnFe2O4@Chitosan was subjected to a pseudo-first-order kinetic model, which can be described as: = (8) Resources 2022, 11, 81 12 of 17 The photodegradation of CIP, AMP and ERY by ZnFe O @Chitosan was subjected to 2 4 a pseudo-first-order kinetic model, which can be described as: In = kt (8) where C and C are the initial and time “t” concentrations of CIP, AMP or ERY, respectively. o t The pseudo-first-order rate constant was calculated from the slope of the graph of 1nC /C o t versus time (Figure 6c) and represented as k, while t is the irradiation time. The pseudo-first- 1 1 1 order rate constant for CIP is 0.035 min , AMP is 0.016 min and ERY is 0.012 min . The values obtained for the pseudo-first-order rate constant is also reflective of the degradation efficiency exhibited by ZnFe O @Chitosan towards the antibiotics. The highest degradation 2 4 efficiency was towards CIP (99.80 0.20%), with the highest rate constant compared to other antibiotics. The higher the rate constant, the faster the process is expected with high degradation efficiency. 3.4. Proposed Mechanism for the Photodegradation of CIP, AMP and ERY by ZnFe O @Chitosan 2 4 Most photocatalytic degradation processes are known to be via reactive oxygen species (ROS) generation within the solution to be degraded. Therefore, the photocatalytic degra- dation exhibited by ZnFe O @Chitosan towards CIP, AMP and ERY was evaluated in 2 4 the presence of IPA to scavenge hydroxyl radical (OH ), AO to scavenge hole (h ) and CH to scavenge superoxide ion radical (O ), as previously reported [38]. The results obtained are presented in Figure 6d. It was observed that the photodegradation efficiency of ZnFe O @Chitosan was reduced in the presence of IPA, AO and CH, indicating that 2 4 they all played roles in the degradation of CIP, AMP and ERY by ZnFe O @Chitosan. 2 4 When CH was introduced into the degradation medium, there was a drastic reduction in the degradation efficiency from 99.80 0.20% to 31.20 0.80% in CIP, 94.50 0.10% to 24.70 0.50% in AMP and 83.20 0.20% to 18.40 0.70% in ERY. A similar observation also took place when AO was introduced into the medium, which suggested the scavenging of hole by AO and superoxide ion radicals by CH during the photodegradation process. This drastic reduction is an indication that both hole and superoxide ion radicals played an important role in the photodegradation process by ZnFe O @Chitosan. 2 4 Furthermore, the reduction in efficiency when IPA was introduced also confirmed that hydroxyl and superoxide ion radicals must have been generated from the photochemical reactions between the hole (h ) and photoexcited electrons (e ) with H O and O molecules 2 2 (Figure 7). As described in Figure 7a, during the process, ZnFe O @Chitosan may have 2 4 absorbed visible-light energy greater than its bandgap, leading to the generation of h in the valence band and e in the conduction band. As long as the recombination of h and e is hindered, the ROS continues to promote the degradation of CIP, AMP or ERY, as described in Figure 7b. 3.5. Re-Useability and Stability of ZnFe O @Chitosan 2 4 The re-useability and stability of a photocatalyst plays an important role in deter- mining its economic viability. In this regard, ZnFe O @Chitosan was regenerated using 2 4 different solvent systems based on the solubility of CIP, AMP and ERY. Solvents used included deionized water, 0.1 M HCl, ethanol or a mixture of ethanol and 0.1 M HCl (3:2). However, a mixture of ethanol and 0.1 M HCl (3:2) gave better results in regen- erating ZnFe O @Chitosan for re-use (Figure 8a). Therefore, at the end of each cycle, 2 4 ZnFe O @Chitosan was washed with a mixture of ethanol and 0.1 M HCl (3:2), dried and 2 4 re-used for the photodegradation of CIP, AMP or ERY. The cycle was repeated until the 15th cycle and the regeneration capacity for 15 successive cycles is shown in Figure 8b. Interest- ingly, the capacity was 97.60 0.10% for CIP, 93.50 0.20% for AMP and 95.00 0.10% for ERY at the 15th cycle, which suggests a high stability of ZnFe O @Chitosan as a vi- 2 4 able photocatalyst for the photodegradation of CIP, AMP and ERY. The ICP–OES results revealed 0.08 ppm of Fe and 0.05 ppm of Zn in the solution after the 15th cycle, which Resources 2022, 11, 81 13 of 17 suggests that the ZnFe O particles leached into solution during the photodegradation 2 4 process. However, the leached amount is within the permissible limits for Fe (0.10 ppm) and Zn (5.00 ppm) in drinking water. The results obtained in this study were also compared with a catalyst previously reported, as shown in Table 1. ZnFe O @Chitosan compared 2 4 favourably with a previously reported photocatalyst for the degradation of CIP, AMP and ERY. Distinctly, ZnFe O @Chitosan exhibited an encouraging stability with capacity above 2 4 90%, even at the 15th regeneration cycle for re-use, which demonstrates the economic viability or advantage of ZnFe O @Chitosan over most recently reported photocatalysts it 2 4 was compared with in the literature. The efficiency towards the degradation of CIP exhib- ited by ZnFe O @Chitosan is higher than values recently reported for Cu O/MoS /rGO 2 4 2 2 (Selvamani et al. 2021) and ZnO [39]. The use of ZnFe O @Chitosan for photodegradation 2 4 Resources 2022, 11, x FOR PEER REwas VIEWconducted in the visible-light regions, which shows that its use does not 14r equir of 19 e an additional cost for a UV source, unlike in the case of some of the previous studies [40–42]. Figure 7. Proposed mechanism for the photodegradation of CIP, AMP and ERY: (a) Scheme for Figure 7. Proposed mechanism for the photodegradation of CIP, AMP and ERY: (a) Scheme for reaction mechanism and (b) Stepwise photodegradation of CIP, AMP and ERY reaction mechanism and (b) Stepwise photodegradation of CIP, AMP and ERY. 3.5. Re-Useability and Stability of ZnFe2O4@Chitosan The re-useability and stability of a photocatalyst plays an important role in determin- ing its economic viability. In this regard, ZnFe2O4@Chitosan was regenerated using differ- ent solvent systems based on the solubility of CIP, AMP and ERY. Solvents used included deionized water, 0.1 M HCl, ethanol or a mixture of ethanol and 0.1 M HCl (3:2). However, a mixture of ethanol and 0.1 M HCl (3:2) gave better results in regenerating ZnFe2O4@Chi- tosan for re-use (Figure 8a). Therefore, at the end of each cycle, ZnFe2O4@Chitosan was washed with a mixture of ethanol and 0.1 M HCl (3:2), dried and re-used for the photo- degradation of CIP, AMP or ERY. The cycle was repeated until the 15th cycle and the regeneration capacity for 15 successive cycles is shown in Figure 8b. Interestingly, the Resources 2022, 11, x FOR PEER REVIEW 15 of 19 capacity was 97.60 ± 0.10% for CIP, 93.50 ± 0.20% for AMP and 95.00 ± 0.10% for ERY at the 15th cycle, which suggests a high stability of ZnFe2O4@Chitosan as a viable photocata- lyst for the photodegradation of CIP, AMP and ERY. The ICP–OES results revealed 0.08 ppm of Fe and 0.05 ppm of Zn in the solution after the 15th cycle, which suggests that the ZnFe2O4 particles leached into solution during the photodegradation process. However, the leached amount is within the permissible limits for Fe (0.10 ppm) and Zn (5.00 ppm) in drinking water. The results obtained in this study were also compared with a catalyst previously reported, as shown in Table 1. ZnFe2O4@Chitosan compared favourably with a previously reported photocatalyst for the degradation of CIP, AMP and ERY. Distinctly, ZnFe2O4@Chitosan exhibited an encouraging stability with capacity above 90%, even at the 15th regeneration cycle for re-use, which demonstrates the economic viability or ad- vantage of ZnFe2O4@Chitosan over most recently reported photocatalysts it was com- pared with in the literature. The efficiency towards the degradation of CIP exhibited by ZnFe2O4@Chitosan is higher than values recently reported for Cu2O/MoS2/rGO (Selvamani et al. 2021) and ZnO [39]. The use of ZnFe2O4@Chitosan for photodegradation Resources 2022, 11, 81 14 of 17 was conducted in the visible-light regions, which shows that its use does not require an additional cost for a UV source, unlike in the case of some of the previous studies [40–42]. Figure 8. (a) Degradation efficiency of ZnFe2O4@Chitosan after washing with solvent systems and Figure 8. (a) Degradation efficiency of ZnFe O @Chitosan after washing with solvent systems and 2 4 (b) Regeneration capacity of ZnFe2O4@Chitosan expressed towards CIP, AMP and ERY at different (b) Regeneration capacity of ZnFe O @Chitosan expressed towards CIP, AMP and ERY at different 2 4 operational cycles. operational cycles. Table 1. Comparison of the photodegradation of CIP, AMP and ERY by ZnFe O @Chitosan with 2 4 other photocatalysts in literature. 1 1 Material Antibiotic DE (%) LIS AC (g L ) Conc (mg L ) Stability (%) Reference Cu O/MoS /rGO CIP 55.00 150 W halogen lamp 0.30 10.00 - [43] 2 2 TiO on glass CIP 92.00 6 W UV-C lamp 1.00 5.00 - [44] ZnO CIP 93.00 8 W Hg fluorescent 0.50 5.00 - [39] ZnO CIP 100.00 9 W Hg UV lamp 0.15 10.00 - [42] MWCNTs- AMP 100.00 36 W UV 0.50 25.00 93.72 (8th cycle) [40] CuNiFe O 2 4 Ru/WO /ZrO AMP 96.00 150 W Xe lamp 1.00 50.00 92.00 (2nd cycle) [41] 3 2 La/Cu/Zr trimetallic AMP 86.00 Sunlight 0.10 50.00 59.00 (6th cycle) [45] Znpc–TiO ERY 74.21 300 W Xe arc lamp 0.40 1 10 M - [46] -Fe O /SiO ERY 87.17 15 W UV-C lamp 0.50 6.00 - [47] 2 3 2 Ag-NP AMP 96.50 Sunlight 0.17 10.00 - [48] FeSi@MN AMP 70.00 Sunlight 0.60 100.00 63.00 (4th cycle) [49] WO3/BiOCl/Chitosan AMP 75.00 Solar light 0.50 * 1 10 67.00 (10th cycle) [50] BiOCl/Chitosan AMP 75.00 Solar light 1.00 * 1 10 67.00 (10th cycle) [51] FeIII-CS-GLA CIP 90.30 Solar light - ** 50 - [52] CIP 99.80 Visible-light 1.00 5.00 97.60 (15th cycle) ZnFe O @Chitosan AMP 94.50 simulation (150 W 1.00 5.00 93.50 (15th cycle) This study 2 4 ERY 83.20 Xe light) 1.00 5.00 95.00 (15th cycle) - = Not reported. Degradation efficiency = DE, Light illumination source = LIS, Amount of catalyst = AC, Conc = Concentration of antibiotic, Nickel-copper ferrite nanoparticles onto multi-walled carbon nanotubes = MWCNTs-CuNiFe O , FeSi@magnetic nanoparticle = FeSi@MN, Ciprofloxacin = CIP, Ampicillin = AMP, 2 4 3 III Erythromycin = ERY, * = mol dm , Fe -CS-GLA = iron (III) chelated cross-linked chitosan, ** = M. Resources 2022, 11, 81 15 of 17 4. Conclusions ZnFe O @Chitosan was prepared by simple chemical process and applied in the 2 4 photodegradation of CIP, AMP and ERY in aqueous solution. The results from the FTIR of ZnFe O @Chitosan revealed prominent peaks, suggesting its synthesis, while signals 2 4 from XRD showed a diffraction pattern confirming the synthesis of ZnFe O @Chitosan 2 4 with a crystallite size of 35.14 nm. The VSM result revealed a saturation magnetization of 2.38 emu g , which is large enough for magnetic separation for practical applications. The study showed that both photodegradation and adsorption were taking place at the same time with the percentage degradation efficiency in the order CIP (99.80 0.20%) > AMP (94.50 0.10%) > ERY (83.20 0.20%). ZnFe O @Chitosan exhibited an encouraging 2 4 stability with capacity above 90%, even at the 15th regeneration cycle. The photodegrada- tion mechanism suggested the role of hydroxyl and superoxide ion radicals. The study revealed ZnFe O @Chitosan to be a promising catalyst for the degradation of CIP, AMP 2 4 and ERY in aqueous solution. Author Contributions: Formal analysis: N.A.H.M., A.A., R.N.S. Investigations: N.A.H.M., A.A., R.N.S. Methodology: N.A.H.M., A.A., R.N.S., S.E. Software: N.A.H.M., R.N.S. Resources: N.A.H.M., A.A., R.N.S. Supervision: A.A., R.N.S., S.E. Writing—original draft: A.A. Writing—review& edit- ing: N.A.H.M., A.A., R.N.S., S.E. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Joint Academy of Scientific Research and Technology — Bibliotheca Alexandrina (ASRT-BA) Research Grants Program (project No. 1325). Data Availability Statement: Not applicable. Acknowledgments: The authors appreciate the support from the Joint Academy of Scientific Research and Technology—Bibliotheca Alexandrina (ASRT-BA) Research Grants Program (project No. 1325), and are also grateful to the Department of Chemistry, University of Cambridge, UK, for analysis. Conflicts of Interest: The authors declare no conflict of interest. References 1. Hanna, N.; Sun, P.; Sun, Q.; Li, X.; Yang, X.; Ji, X.; Zou, H.; Ottoson, J.; Nilsson, L.E.; Berglund, B.; et al. Presence of antibiotic residues in various environmental compartments of Shandong province in eastern China: Its potential for resistance development and ecological and human risk. Environ. Int. 2018, 114, 131–142. [CrossRef] [PubMed] 2. Zalewska, M.; Błazejewska, ˙ A.; Czapko, A.; Popowska, M. 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Journal
Resources – Multidisciplinary Digital Publishing Institute
Published: Sep 22, 2022
Keywords: adsorption; antibiotics; catalysis; ferrite; photodegradation