RSC Advances

Bakkar, Ashraf; Seleman, Mohamed M. El-Sayed; Ahmed, Mohamed M. Zaky; Harb, Saeed; Goren, Sami; Howsawi, Eskander

doi: 10.1039/d3ra00289fpmid: 36824230

Heavy oil fly ash “HOFA” is the fly ash generated in power stations using heavy oil as fuel. HOFA is considered a hazardous waste because it contains considerable amounts of heavy metals. However, it contains significant amounts of vanadium “V” and nickel “Ni”, which are precious metals for manufacturing processes. This paper presents a critical review of various approaches described in the literature for the recovery of V and Ni from HOFA, including processes of leaching, chemical precipitation, solvent extraction, and ion exchange. The optimum operational parameters and their effects on recovery efficiency are discussed. The digestion mixtures of strong mineral acids used for dissolving all metals present in HOFA are also highlighted. The leaching processes of V and Ni use mainly acidic and alkaline solutions. Bioleaching is a promising environmentally friendly approach for the recovery of V and Ni through using appropriate bacteria and fungi. After leaching, V and Ni compounds are recovered and purified using various techniques, including chemical precipitation, solvent extraction, and ion exchange. In most cases, V and Ni are recovered as thermally decomposable compounds that undergo calcination to produce V2O5 and NiO. Eventually, V and Ni are recovered as pure oxides in most approaches, but pure metals are obtained in exceptional procedures.

Wu, Lina; Wang, Huiping; Kong, Xiangqian; Wei, Haibo; Chen, Sheng; Chi, Lisheng

doi: 10.1039/d2ra07757dpmid: 36824231

Effective removal of strontium isotopes in radioactive waste streams has important implications for the environment and the sustainable development of nuclear energy. In this work, a zirconium phosphate/18-crown-ether-6 (ZrP/18C6) composite was prepared using the intercalation method by loading crown ether into zirconium phosphate. The composite was structurally and morphologically characterized by XRD, FT-IR, XPS, and SEM. The adsorption experiments of Sr2+ onto the ZrP/18C6 composite were conducted as a function of temperature, pH, Sr2+ concentration and competing ions. The results indicate ZrP/18C6 can adsorb 98.6% of Sr2+ within 30 minutes at an Sr2+ concentration of 100 mg L−1 and maintain a high removal rate with a distribution coefficient of 7 × 105 mL g−1 when Sr2+ is at a low level of 4.28 mg L−1. The ZrP/18C6 composite reached a maximum adsorption capacity of 195.74 mg g−1 at an Sr2+ concentration of 380 mg L−1, which is significantly higher than the 43.03 mg g−1 of α-ZrP. The adsorption performance of Sr2+ onto ZrP/18C6 is not significantly affected by temperature, pH and competing ions. Furthermore, the adsorption kinetics and thermodynamics were analyzed based on the adsorption data obtained in the present work. It is shown that the adsorption of Sr2+ onto ZrP/18C6 follows the pseudo-second-order model and the Langmuir monolayer model, respectively. Additionally, the adsorption mechanism of Sr2+ by ZrP/18C6 is discussed.

Ashrafi, Mona; Farhadi, Saeed

doi: 10.1039/d2ra07898hpmid: 36845582

In this work, a magnetic H3PW12O40/Fe3O4/MIL-88A (Fe) rod-like nanocomposite as a stable and effective ternary adsorbent was fabricated by the hydrothermal method and utilized for the removal of ciprofloxacin (CIP), tetracycline (TC) and organic dyes from aqueous solution. Characterization of the magnetic nanocomposite was accomplished by FT-IR, XRD, Raman spectroscopy, SEM, EDX, TEM, VSM, BET specific surface area and zeta potential analyses. The influencing factors on the adsorption potency of the H3PW12O40/Fe3O4/MIL-88A (Fe) rod-like nanocomposite including initial dye concentration, temperature and adsorbent dose were studied. The maximum adsorption capacities of H3PW12O40/Fe3O4/MIL-88A (Fe) for TC and CIP were 370.37 mg g−1 and 333.33 mg g−1 at 25 °C, respectively. In addition, the H3PW12O40/Fe3O4/MIL-88A (Fe) adsorbent had high regeneration and reusability capacity after four cycles. In addition, the adsorbent was recovered through magnetic decantation and reused for three consecutive cycles without a considerable reduction in its performance. The adsorption mechanism was mainly ascribed to electrostatic and π–π interactions. According to these results, H3PW12O40/Fe3O4/MIL-88A (Fe) can act as a reusable effective adsorbent for the fast elimination of tetracycline (TC), ciprofloxacin (CIP) and cationic dyes from aqueous solutions.

Wang, Liquan; Li, Ruyi; Zhang, Yimin; Gao, Yuexiang; Xiao, Xian; Zhang, Zhiwei; Chen, Ting; Zhao, Yuan

doi: 10.1039/d3ra00345kpmid: 36845579

In this study, oxygen-doped carbon nitride (O–C3N4) was prepared by thermal polymerization and was applied to activate peroxymonosulfate (PMS) for tetracycline (TC) degradation. Experiments were performed to comprehensively evaluate the degradation performance and mechanism. The oxygen atom replaced the nitrogen atom of the triazine structure, which improves the specific surface area of the catalyst, enriches the pore structure and achieves higher electron transport capacity. The characterization results showed that 0.4 O–C3N4 had the best physicochemical properties, and the degradation experiments showed that the 0.4 O–C3N4/PMS system had a higher TC removal rate in 120 min (89.94%) than the unmodified graphitic-phase C3N4/PMS system (52.04%). Cycling experiments showed that O–C3N4 has good reusability and structural stability. Free radical quenching experiments showed that the O–C3N4/PMS system had free radical and non-radical pathways for TC degradation and that the main active species was singlet oxygen (1O2). Intermediate product analysis showed that TC was mineralized to H2O and CO2 mainly by the ring opening, deamination, and demethylation reactions. The results of this study show that the 0.4 O–C3N4/PMS system is simple to prepare and is efficient at removing TC from contaminated water.

Du, Bo; Hu, Yuting; Cheng, Ting; Jiang, Zhaozhong; Wang, Zhenzhen; Zhu, Chengzhu

doi: 10.1039/d3ra00235gpmid: 36845597

A series of Fe-modified β-MnO2 (FeOx/β-MnO2) composite catalysts were prepared by an impregnation method with β-MnO2 and ferro nitrate as raw materials. The structures and properties of the composites were systematically characterized and analyzed by X-ray diffraction, N2 adsorption–desorption, high-resolution electron microscopy, temperature-programmed reduction of H2, temperature-programmed desorption of NH3, and FTIR infrared spectroscopy. The deNOx activity, water resistance, and sulfur resistance of the composite catalysts were evaluated in a thermally fixed catalytic reaction system. The results indicated that the FeOx/β-MnO2 composite (Fe/Mn molar ratio of 0.3 and calcination temperature of 450 °C) had higher catalytic activity and a wider reaction temperature window compared with β-MnO2. The water resistance and sulfur resistance of the catalyst were enhanced. It reached 100% NO conversion efficiency with an initial NO concentration of 500 ppm, a gas hourly space velocity of 45 000 h−1, and a reaction temperature of 175–325 °C. The appropriate Fe/Mn molar ratio sample had a synergistic effect, affecting the morphology, redox properties, and acidic sites, and helped to improve the low-temperature NH3-SCR activity of the composite catalyst.

Wen, Long; Wang, Jianfang; Liu, Zhuoliang; Tao, Cheng-an; Rao, Jialing; Hang, Jian; Li, Yujiao

doi: 10.1039/d2ra05383gpmid: 36874943

A portable acetylcholinesterase (AChE)-based electrochemical sensor based on a screen-printed carbon electrode (SPCE) and a miniature potentiostat was constructed for the rapid field detection of organophosphorus pesticides (OPs). Graphene (GR) and gold nanoparticles (AuNPs) were successively introduced onto SPCE for surface modification. Due to the synergistic effect of the two nanomaterials, the signal of the sensor has a significant enhancement. Take isocarbophos (ICP) as a model for chemical warfare agents (CAWs) and Ops; the SPCE/GR/AuNPs/AChE/Nafion sensor shows a wider linear range (0.1–2000 μg L−1), and a lower limit of detection (0.012 μg L−1) than SPCE/AChE/Nafion and SPCE/GR/AChE/Nafion sensors. Tests in actual fruit and tap water samples also yielded satisfactory results. Therefore, the proposed method can be used as a simple and cost-effective strategy for construction of portable electrochemical sensors for OP field detection.

Imali, D. Yureka; Perera, E. Chavin J.; Kaumal, M. N.; Dissanayake, Dhammike P.

doi: 10.1039/d3ra00009epmid: 36845598

This work presents a highly sensitive, economical, flexible, and disposable humidity sensor developed with a facile fabrication process. The sensor was fabricated on cellulose paper using polyemaraldine salt, a form of polyaniline (PAni), via the drop coating method. A three-electrode configuration was employed to ensure high accuracy and precision. The PAni film was characterized using various techniques including ultraviolet-visible (UV-vis) absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The humidity sensing properties were evaluated through electrochemical impedance spectroscopy (EIS) in a controlled environment. The sensor exhibits a linear response with R2 = 0.990 for impedance over a wide range of (0%–97%) relative humidity (RH). Further, it displayed consistent responsiveness, a sensitivity of 1.1701 Ω/%RH, acceptable response (≤220 s)/recovery (≤150 s), excellent repeatability, low hysteresis (≤2.1%) and long-term stability at room temperature. The temperature dependence of the sensing material was also studied. Due to its unique features, cellulose paper was found to be an effective alternative to conventional sensor substrates according to several factors including compatibility with the PAni layer, flexibility and low cost. These unique characteristics make this sensor a promising option for use in specific healthcare monitoring, research activities, and industrial settings as a flexible and disposable humidity measurement tool.

Liao, Yiju; Aspin, Alexandria; Yang, Ziming

doi: 10.1039/d3ra90014bpmid: 36845589

Correction for ‘Anaerobic oxidation of aldehydes to carboxylic acids under hydrothermal conditions’ by Yiju Liao et al., RSC Adv., 2022, 12, 1738–1741, https://doi.org/10.1039/D1RA08444E.

Baumann, Viktoria; Popa, Karin; Cologna, Marco; Rivenet, Murielle; Walter, Olaf

doi: 10.1039/d3ra00487bpmid: 36845592

We report on the crystallite growth of nanometric NpO2 and UO2 powders. The AnO2 nanoparticles (An = U and Np) were synthesized by hydrothermal decomposition of the corresponding actinide(IV) oxalates. NpO2 powder was isothermally annealed between 950 °C and 1150 °C and UO2 between 650 °C and 1000 °C. The crystallite growth was then followed by high-temperature X-ray diffraction (HT-XRD). The activation energies for the growth of crystallites of UO2 and NpO2 were determined to be 264(26) kJ mol−1 and 442(32) kJ mol−1, respectively, with a growth exponent n = 4. The value of the exponent n and the low activation energy suggest that the crystalline growth is rate-controlled by the mobility of the pores, which migrate by atomic diffusion along the pore surfaces. We could thus estimate the cation self-diffusion coefficient along the surface in UO2, NpO2 and PuO2. While data for surface diffusion coefficients for NpO2 and PuO2 are lacking in the literature, the comparison with literature data for UO2 supports further the hypothesis of a surface diffusion controlled growth mechanism.

Zulfajri, Muhammad; Sudewi, Sri; Damayanti, Rizki; Huang, Genin Gary

doi: 10.1039/d2ra07620apmid: 36845584

In this study, new nitrogen-doped carbon dots (N-CDs) were prepared by utilizing rambutan seed waste and L-aspartic acid as dual precursors (carbon and nitrogen sources) through a hydrothermal treatment method. The N-CDs showed blue emission in solution under UV light irradiation. Their optical and physicochemical properties were examined via UV-vis, TEM, FTIR spectroscopy, SEM, DSC, DTA, TGA, XRD, XPS, Raman spectroscopy, and zeta potential analyses. They showed a strong emission peak at 435 nm and excitation-dependent emission behavior with strong electronic transitions of CC/CO bonds. The N-CDs exhibited high water dispersibility and great optical properties in response to some environmental conditions such as heating temperature, light irradiation, ionic strength, and storage time. They have an average size of 3.07 nm and good thermal stability. Owing to their great properties, they have been used as a fluorescent sensor for Congo red dye. The N-CDs selectively and sensitively detected Congo red dye with a detection limit of 0.035 μM. Moreover, the N-CDs were utilized to detect Congo red in tap and lake water samples. Thus, rambutan seed waste was successfully converted into N-CDs and these functional nanomaterials are promising for use in important applications.