Comparative study of photocatalytic activities of Zn5(OH)8Cl2·H2O and ZnO nanostructures in ciprofloxacin degradation: Response surface methodology and kinetic studies

The Z-Scheme MIL-88B(Fe)/BiOBr Heterojunction Promotes Fe(III)/Fe(II) Cycling and Photocatalytic-Fenton-Like Synergistically Enhances the Degradation of Ciprofloxacin

The Z-scheme MIL-88B/BiOBr (referred to as MxBy, whereas x and y are the mass of MIL-88B(Fe) and BiOBr) heterojunction photocatalysts are successfully prepared by a facile ball milling method. By adding low concentration H2O2 under visible light irradiation, the Z-scheme heterojunction and photocatalytic-Fenton-like reaction synergistically enhance the degradation and mineralization of ciprofloxacin (CIP). Among them, M50B150 showed efficient photodegradation efficiency and excellent cycling stability, with 94.6% removal of CIP (10 mg L-1) by M50B150 (0.2 g L-1) under 90 min of visible light. In the MxBy heterojunctions, the rapid transfer of photo-generated electrons not only directly decomposed H2O2 to generate ·OH, but also improved the cycle of Fe3+/Fe2+ pairs, which facilitated the reaction with H2O2 to generate ·OH and ·O2 - radicals. In addition, the effects of photocatalyst dosages, pH of CIP solution, and coexisting substances on CIP removal are systematically investigated. It is found that the photocatalytic- Fenton-like reaction can be carried out at a pH close to neutral conditions. Finally, the charge transfer mechanism of the Z-scheme is verified by electron spin resonance (ESR) signals. The ecotoxicity of CIP degradation products is estimated by the T.E.S.T tool, indicating that the constructed photocatalysis-Fenton-like system is a green wastewater treatment technology.

Composite RGO/Ag/Nanosponge Materials for the Photodegradation of Emerging Pollutants from Wastewaters

Some composite materials have been prepared, constituted by a cyclodextrin-bis-urethane-based nanosponge matrix in which a reduced graphene oxide/silver nanoparticles photocatalyst has been dispersed. Different chain extenders were employed for designing the nanosponge supports, in such a way as to decorate their hyper-cross-linked structure with diverse functionalities. Moreover, two different strategies were explored to accomplish the silver loading. The obtained systems were successfully tested as catalysts for the photodegradation of emerging pollutants such as model dyes and drugs. Enhancement of the photoactive species performance (up to nine times), due to the synergistic local concentration effect exerted by the nanosponge, could be assessed. Overall, the best performances were shown by polyamine-decorated materials, which were able to promote the degradation of some particularly resistant drugs. Some methodological issues pertaining to data collection are also addressed.

Photocatalytic performance of 3D engineered chitosan hydrogels embedded with sulfur-doped C3N4/ZnO nanoparticles for Ciprofloxacin removal: Degradation and mechanistic pathways

Ciprofloxacin, a biotoxic micropollutant, is ubiquitously found in the water environment, which is a global concern. This study developed polymeric S-C3N4/ZnO-Chitosan (indexed as SCZ-CH) hydrogels for degrading Ciprofloxacin. The SCZ-CH hydrogels provided the Ciprofloxacin degradation efficiencies of ~93% and ~69% in UV and visible lights, respectively, at optimum conditions (SCZ-CH hydrogels with 2 g/L SCZ, 20 mg/L initial concentration, pH 5, and room temperature). In addition, immobilized SCZ-CH hydrogels structures enable easy separation of the SCZ catalyst from water. The spectroscopic and microscopic analyses of SCZ-CH hydrogels show multifaceted properties, like high oxygen concentrations, crystallinity, stacked structure, high roughness, and improved bandgap energy, which are responsible for the enhanced photocatalytic activity. The effects of water matrix and experimental conditions on Ciprofloxacin degradation were also studied, which suggested that the catalyst dose and solution pH have significant effects on photocatalytic activity. SCZ-CH hydrogels have shown good mineralization efficiency (~98%) and reusability (up to 10 cycles) for Ciprofloxacin removal. Superoxide radicals played an essential role in the degradation of Ciprofloxacin. The Ciprofloxacin molecules get degraded by driving radicals through oxidation, defluorination, substitution, and breaking of the rings. The proposed SCZ-CH hydrogels can be effectively used at a large scale to treat micropollutants.

A heterogeneous peroxymonosulfate catalyst built by Fe-based metal-organic framework for the dye degradation

The regulatory control on dyes is an important issue, as their discharge into the environment can pose significant risks to human health. MIL-101(Fe) prepared by a solvothermal method was used as a catalyst to generate sulfate (SO₄^•-) and hydroxyl (HO^•) radicals from peroxymonosulfate (PMS) for the treatment of orange G (OG). The structural properties of MIL-101(Fe) were assessed by a number of characterization approaches (e.g., Fourier-transform infrared spectroscopy). The factors controlling the removal of OG were explored by a response surface methodology with central composite design (RSM-CCD) plus adaptive neuro-fuzzy inference system (ANFIS). The synthetized MIL-101(Fe) had uniform octahedral nanocrystals with rough surfaces and porous structures. The maximum catalytic removal efficiency of OG with MIL-101(Fe)/PMS process was 74% (the final concentration of Fe²⁺ as 0.19 mg/L and reaction rate of 434.2 μmol/g/h). The catalytic removal of OG could be defined by the non-linear kinetic models based on RSM. The OG removal efficiency declined noticeably with the addition of radical scavengers such as ethanol (EtOH) and tert-butanol (TBA) along with some mineral anions. Accordingly, MIL-101(Fe)/PMS is identified as an effective remediation option for the dyes based on advanced oxidation process (AOPs) based on high treatment efficiency at low dosage of low cost catalyst.

ZnO-Activated Carbon Blended as a Catalyst for Oxidative Desulfurization of Dibenzothiophene

The problem of sulfur content in heavy oil is a challenge for researchers to meet the needs of environmentally friendly fuels. The catalyst preparation plays an important role in the desulfurization process. The synthesis of ZnO-activated carbon as a catalyst and its activity in oxidative desulfurization (ODS) reaction has been successfully carried out. In this work, the ZnO and activated carbon (AC) were blended by a solid-solid reaction. The ZnO, AC, and ZnO-AC were then characterized using acidity test with pyridine vapor adsorption, Fourier Transform Infra-Red (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX), and Surface Area Analyzer (SAA). ODS of dibenzothiophene (DBT) reaction was performed by using H2O2 under variation of the reaction time (30, 60, 120, and 150 min) for the ZnO-AC catalyst. The efficiency of ODS-DBT was analyzed by a UV-Visible spectrophotometer. The XRD analysis result showed that ZnO-AC blended displays new crystal peaks of Zn in the AC diffractogram. The surface area (734.351 m2/g) and acidity (4.8780 mmol/g) of ZnO-AC were higher than ZnO and AC themselves. ZnO-AC produced the highest efficiency of ODS-DBT which was 93.83% in the reaction time of 120 min. Therefore, the simple procedure of this physical blending was proved effective to homogenize between ZnO and AC into ZnO-AC so that it has good physicochemical properties as an ODS-DBT catalyst. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Adsorption and detoxification of pharmaceutical compounds from wastewater using nanomaterials: A review on mechanism, kinetics, valorization and circular economy

Antibiotics overuse, inappropriate conduct, and discharge have led to adverse effects on various ecosystems. The occurrence of antibiotics in surface and drinking water is a matter of global concern. It is responsible for multiple disorders, including disruption of endocrine hormones and high chronic toxicity. The hospitals, pharmaceutical industries, households, cattle farms, and aquaculture are the primary discharging sources of antibiotics into the environment. This review provides complete detail on applying different nanomaterials or nanoparticles for the efficient removal of antibiotics from the diverse ecosystem with a broader perspective. Efforts have been made to focus on the degradation pathways and mechanism of antibiotic degradation using nanomaterials. More light has been shed on applying nanostructures in photocatalysis, which would be an economical and efficient solution. The nanoscale material or nanoparticles have incredible potential for mineralizing pharmaceutical compounds in aqueous solutions at low cost, easy handling characteristics, and high efficacy. Furthermore, nanoparticles can absorb the pharmaceutical by-products and wastes at a minimum cost as they can be easily recycled. With the increasing number of research in this direction, the valorization of pharmaceutical wastes and by-products will continue to expand as we progress from old conventional approaches towards nanotechnology. The utilization of nanomaterials in pharmaceutical wastewater remediation is discussed with a major focus on valorization, energy generation, and minimization and its role in the circular economy creating sustainable development.

Removal of SO2 from smelting flue gas by using copper tailings with MnSO4: factors optimization by response surface methodology

The abatement of SO₂ and the utilization of copper tailings are identified as two attention-attracting environmental issues in the copper smelter. In this study, to improve the flue gas desulfurization performance and the utilization of copper tailings, SO₂ removal from smelting flue gas by using copper tailings combined with MnSO₄·H₂O was investigated. The effects of operation variables, including inlet SO₂ concentration, absorption temperature, slurry concentration, and MnSO₄·H₂O amount, on the flue gas desulfurization performance were studied based on the response surface method. It was found that the effect of operation variables on SO₂ removal follows the descending order: the inlet SO₂ concentration, MnSO₄·H₂O concentration, absorbent temperature, and solid-liquid ratio. The interaction between the inlet SO₂ concentration and MnSO₄·H₂O concentration is an important factor for breakthrough sulfur capacity. Elevated temperature and high initial SO₂ concentration inhibited the efficient removal of SO₂. Moreover, a proposed equation exhibits good consistency in the prediction for the breakthrough sulfur dioxide capacity. Therefore, the results can provide a reliable reference and basis for industrial application for flue gas desulfurization with copper tailings.

Predicting the trend and utility of different photocatalysts for degradation of pharmaceutically active compounds: A special emphasis on photocatalytic materials, modifications, and performance comparison

The rapid rise in the healthcare sector has led to an increase in pharmaceutically active compounds (PhACs) in different aqueous bodies. The toxicity of the PhACs and their ability to persist after conventional treatment processes have escalated research in the field of photocatalytic treatment. Although different photocatalysts have been successful in degrading PhACs, their inherent drawbacks have severely limited their application on a large scale. A substantial amount of research has been aimed at overcoming the high cost of the photocatalytic material, low quantum yield, the formation of toxic end products, etc. Hence, to further research in this field, researchers must have a fair idea of the current trends in the application of different photocatalysts. In this article, the trends in the use of various photocatalysts for the removal of different PhACs have been circumscribed. The performance of different groups of photocatalysts to degrade PhACs from synthetic and real wastewater has been addressed. The drawbacks and advantages of these materials have been compared, and their future in the field of PhACs removal has been predicted using S-curve analysis. Zinc and titanium-based photocatalysts were efficient under UV irradiation, while bismuth and graphene-based materials exhibited exemplary performance in visible light. However, iron-based compounds were found to have the most promising future, which may be because of their magnetic properties, easy availability, low bandgap, etc. Different modification techniques, such as morphology modification, doping, heterojunction formation, etc., have also been discussed. This study may help researchers to clarify the current research status in the field of photocatalytic treatment of PhACs and provide valuable information for future research.

Chemical speciation of ciprofloxacin in aqueous solution regulates its phytotoxicity and uptake by rice (Oryza sativa L.)

Ciprofloxacin (CIP), a widely used fluoroquinolone antibiotic, is frequently detected in aqueous environments, and could be assimilated by vegetable plants to possess potential threats to human and animal health through food chains. However, plant uptake of CIP in different chemical speciation has still far from clear now. Thus, the toxicity and uptake of CIP by rice plants were investigated under different solution pH, owing to its contribution to different chemical speciation of CIP. Results display that high pH-driven changes of CIP from cation (CIP⁺) to anion (CIP^-) decreased its adsorption and uptake by excised roots and intact plants, respectively. However, CIP concentrations in roots, stems and leaves all exhibited no significant differences with increasing solution pH. Moreover, six intermediates of CIP were detected and two possible transformation pathways were proposed in rice plants, including firstly oxidation and following consecutive cleavage of piperazine ring. After accumulated in plant tissues, CIP significantly inhibited the plant growth, decreased the photosynthetic pigments contents and enhanced the antioxidant enzyme activities in a concentration-dependent manner. Besides, high pH exacerbated the growth inhibition and changed the oxidative damage responses of rice plants to CIP. These findings indicate that the uptake and toxicity of CIP in rice plants were influenced by solution pH-driven changes of its chemical speciation.

A multivariate modeling and experimental realization of photocatalytic system of engineered S-C3N4/ZnO hybrid for ciprofloxacin removal: Influencing factors and degradation pathways

Ciprofloxacin, a pharmaceutically active compound, is present as a micropollutant in wastewater, which cannot be removed by conventional techniques due to its recalcitrant nature. Therefore, in the present study, the photocatalytic degradation of this bio-toxic compound was demonstrated using a three-dimensional sulfur-doped graphitic-carbon nitride/zinc oxide hybrid, with enriched oxygen vacancies. The influence of various water matrices and experimental conditions on the ciprofloxacin degradation was optimized. The hybrid material showed 98.8% and 75.8% degradation efficiency under optimum experimental conditions (i.e., catalyst dose: 1 g/L; pH: 5; initial ciprofloxacin concentration: 20 mg/L; temperature: 27 °C) under ultraviolet (UV) and visible light, respectively. A neural-network-based multivariate approach was used to predict a significant model considering the experimental conditions that showed adequate statistical significance (R²: 0.992 and F-value: 8707.1). The relative significance of the experimental conditions was assessed, suggesting that the initial ciprofloxacin concentration has a more significant effect on the degradation efficiency than the other factors. The rate kinetics and reaction mechanisms for ciprofloxacin degradation were demonstrated, and the driving radicals involved were identified. A higher rate of reaction was found under UV irradiation (0.01702 min^-1) than under visible light (0.00802 min^-1). Superoxide radicals were identified as the main driving radicals, which caused substantial photocatalytic reactions among the hybrid and ciprofloxacin molecules. Microscopic and macroscopic analyses of the used hybrid were conducted, which confirmed the presence of higher defect concentrations, crystallinity, and interlinked stacked structure in the hybrid. Hence, the 3D hybrid can be efficiently used and reused for ciprofloxacin degradation. This advanced photocatalytic system can be widely used to remediate emerging contaminants in wastewater treatment.

Electron paramagnetic resonance and microstructural insights into the thermal behavior of simonkolleite nanoplatelets

The thermal decomposition process of simonkolleite, at 500 °C was monitored by EPR and electron microscopy. The experimental data indicate that after an 1 h at 500 °C, three morphologies can be observed from the thermal decomposition of ZHC.

Degradation of 1,2-dichloroethane by photocatalysis using immobilized PAni-TiO2 nano-photocatalyst

1,2-Dichloroethane is one of the most hazardous environmental pollutants in wastewaters. It is mainly used to produce vinyl chloride monomer, the major precursor for PVC production. It is determined to be a probable human carcinogen and has been listed as a priority pollutant by the United States Environmental Protection Agency. Due to high chemical stability and low biodegradability of 1,2-dichloroethane, heterogeneous photocatalysis was used for degradation of this chlorinated hydrocarbon. PAni-TiO₂ nanocomposite was synthesized by in situ deposition oxidative polymerization method and immobilized on glass beads by a modified dip coating and heat attachment method. The characteristics of synthesized PAni-TiO₂ nanoparticles were confirmed using the results of morphology tests including Fourier-transform infrared spectra, X-ray diffraction patterns, particle size analysis, UV-Visible spectrophotometer, scanning electron microscope, and energy-dispersive X-ray spectroscopy. The performance of photocatalytic degradation of 1,2-dichloroethane using synthesized PAni-TiO₂ nanocomposite in a designed and constructed pilot scale packed bed recirculating photocatalytic reactor under xenon light irradiation was investigated. The response surface methodology based on the central composite design was used to evaluate and optimize the effect of 1,2-dichloroethane concentration, residence time, pH, and coating mass as independent variables on the photocatalytic degradation of 1,2-dichloroethane as the response function. Results showed that actual and predicted results were well fitted with R² of 0.9870, adjusted R² of 0.9718, and predicted R² of 0.9422. The optimum conditions for 1,2-dichloroethane photocatalytic degradation were the 1,2-dichloroethane concentration of 250 mg/L, the residence time of 240 min, pH of 5, and coating mass of 0.5 mg/cm², which resulted in 88.84% photocatalytic degradation. Kinetic of the photocatalytic degradation at optimal condition follows the Langmuir-Hinshelwood first-order reaction with k = 0.0095 min^-1 with R² = 0.9455. Complete photocatalytic degradation of 1,2-DCE was achieved after 360 min.

Removal of antibiotics from aqueous solutions by nanoparticles: a systematic review and meta-analysis

Antibiotics, as one of the emerging pollutants, are non-biodegradable compounds and long-term exposure to them may affect endocrine, hormonal, and genetic systems of human beings, representing a potential risk for both the environment and human health. The presence of antibiotics in surface waters and drinking water causes a global health concern. Many researches have stated that conventional methods used for wastewater treatment cannot fully remove antibiotic residues, and they may be detected in receiving waters. It is reported that nanoparticles could remove these compounds even at low concentration and under varied conditions of pH. The current study aimed to review the most relevant publications reporting the use of different nanoparticles to remove antibiotics from aqueous solutions. Moreover, meta-analysis was conducted on the results of some articles. Results of meta-analysis proved that different nanoparticles could remove antibiotics with an acceptable efficiency of 61%. Finally, this review revealed that nanoparticles are promising and efficient materials for degradation and removal of antibiotics from water and wastewater solutions. Furthermore, future perspectives of the new generation nanostructure adsorbents were discussed in this study.

Synthesis of Nano-Zinc Oxide Loaded on Mesoporous Silica by Coordination Effect and Its Photocatalytic Degradation Property of Methyl Orange

Salicylaldimine-modified mesoporous silica (Sal-MCM-3 and Sal-MCM-9) was prepared through a co-condensation method with different amounts of added salicylaldimine. With the coordination from the salicylaldimine, zinc ions were impregnated on Sal-MCM-3 and Sal-MCM-9. Then, Zn-Sal-MCM-3 and Zn-Sal-MCM-9 were calcined to obtain nano-zinc oxide loaded on mesoporous silica (ZnO-MCM-3 and ZnO-MCM-9). The material structures were systematically studied by Fourier transform infrared spectroscopy (FTIR), N₂ adsorption/desorption measurements, X-ray powder diffraction (XRD), zeta potential, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet diffused reflectance spectrum (UV-vis DRS), and thermogravimetry (TGA). Methyl orange (MO) was used to investigate the photocatalysis behavior of ZnO-MCM-3 and ZnO-MCM-9. The results confirmed that nano ZnO was loaded in the channels as well as the outside surface of mesoporous silica (MCM-41). The modification of salicylaldimine helped MCM-41 to load more nano ZnO on MCM-41. When the modification amount of salicylaldimine was one-ninth and one-third of the mass of the silicon source, respectively, the load of nano ZnO on ZnO-MCM-9 and ZnO-MCM-3 had atomic concentrations of 1.27 and 2.03, respectively. ZnO loaded on ZnO-MCM-9 had a wurtzite structure, while ZnO loaded on ZnO-MCM-3 was not in the same crystalline group. The blocking effect caused by nano ZnO in the channels reduced the orderliness of MCM-41. The photodegradation of MO can be divided in two processes, which are mainly controlled by the surface areas of ZnO-MCM and the loading amount of nano ZnO, respectively. The pseudo-first-order model was more suitable for the photodegradation process.

Cr(OH)3-NPs-CNC hybrid nanocomposite: a sorbent for adsorptive removal of methylene blue and malachite green from solutions

In this article, Cr(OH)₃ nanoparticle-modified cellulose nanocrystal (CNC) as a novel hybrid nanocomposite (Cr(OH)₃-NPs-CNC) was prepared by a simple procedure and used as a sorbent for adsorptive removal of methylene blue (MB) and malachite green (MG) from aqueous solution. Different kinetic models were tested, and the pseudo-second-order kinetic model was found more suitable for the MB and MG adsorption processes. The BET and Langmuir models were more suitable for the adsorption processes of MB and MG. Thermodynamic studies suggested that the adsorption of MB and MG onto Cr(OH)₃-NPs-CNC nanocomposite was a spontaneous and endothermic process. The maximum adsorption capacities for MB and MG were reached 106 and 104 mg/g, respectively, which were almost two times higher than unmodified CNC. The chemical stability and leaching tests of the Cr(OH)₃-NPs-CNC hybrid nanocomposite showed that only small amounts of chromium were leached into the solution.