Optimizing the fabrication of nano-plasmonic silver‑nitrogen co-doped zinc oxide (Ag x Zn (1-x) N y O (1-y) ) mediated by ammonia template: Insight into its enhanced physiochemical and photocatalytic behavior

Preparation and characterization of N-doped ZnO and N-doped TiO2 beads for photocatalytic degradation of phenol and ammonia

N-doped ZnO beads (NZB) and N-doped TiO₂ beads (NTB) were synthesized via a modified sol-gel technique utilizing chitosan (CS)/polyvinyl alcohol (PVA) hydrogel beads as basic support for photocatalyst. Urea was used as a source of nitrogen in the preparation of N-doped ZnO beads, while ammonium acetate, CH₃COONH₄, was used as a nitrogen source in the production of N-doped TiO₂ beads. The characteristics of synthesized beads were identified by scanning electron microscope (SEM), X-ray photoelectron spectroscopy analysis (XPS), X-ray diffraction (XRD), N₂ adsorption-desorption isotherms, BET surface area, Fourier transform infrared (FT-IR) measurements, and diffuse reflectance spectroscopy (DRS) studies. The use of the nitrogen doping method for photocatalyst was performed to adjust the bandgap and electrical properties of ZnO and TiO₂ by establishing acceptor defects. NZB and NTB with the intrinsic donor defect of oxygen vacancy and the nitrogen-to-oxygen acceptor defect could be activated by a less-energy UV consumption for efficient pollutant degradation. The results indicated that the as-synthesized NZB achieved much higher degradation activity than NTB, commercial ZnO, and TiO₂ in the decomposition of a binary mixture composed of ammonia and phenol under UV light irradiation.

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.

Tailored functional materials as robust candidates to mitigate pesticides in aqueous matrices-a review

Pesticides are among the top-priority contaminants, which significantly contribute to environmental deterioration. Conventional techniques are not efficient enough to remove pollutants from environmental matrices. The development of functional materials has emerged as promising candidates to remove and degrade pesticides and related hazardous compounds. Furthermore, the nanohybrid materials with unique structural and functional characteristics, such as better material anchorage, mass transfer, electron-hole separation, and charged interaction make them a versatile option to treat and reduce pollutants from aqueous matrices. Herein, we present the current progress in the development of functional materials for the abatement of toxic pesticides. The physicochemical characteristics and pesticide-removal functionalities of various metallic functional materials (e.g., zirconium, zinc, titanium, tungsten, and iron), polymer, and carbon-based materials are critically discussed with suitable examples. Finally, the industrial-scale applications of the functional materials, concluding remarks, and future directions in this important arena are given.

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.

Photo-induced degradation of bio-toxic Ciprofloxacin using the porous 3D hybrid architecture of an atomically thin sulfur-doped g-C3N4/ZnO nanosheet

Ciprofloxacin is a pharmaceutically active compound which belongs to a class of micropollutants that cannot be removed using conventional water treatment systems. In this study, photocatalytic degradation using materials with high surface area and active sites was proposed to remove such contaminants. We demonstrated an easily scalable and simple synthesis route to prepare a 3D porous sulfur-doped g-C₃N₄/ZnO hybrid material, and the preparation process parameters were optimized using response surface methodology targeting Ciprofloxacin degradation. The hybrid material removed up to 98% of the bio-toxic Ciprofloxacin from synthetic water. The porous, defect engineered, thermally stable, and chemically interconnected hybrid material presented an 18 and 38% improved degradation efficiency compared to ZnO and sulfur-doped g-C₃N₄ (or S-C₃N₄), respectively. Based on our experimental results, an empirical relation correlating synthesis process parameters and degradation efficiency was developed using face-centered central composite design (FCCD) and response surface methodology (RSM). The current model can be used to design catalytic materials for removing bio-toxic and other micropollutants from water.

Pharmaceutically active compounds in aqueous environment: A status, toxicity and insights of remediation

Pharmaceutically active compounds (PhACs) have pernicious effects on all kinds of life forms because of their toxicological effects and are found profoundly in various wastewater treatment plant influents, hospital effluents, and surface waters. The concentrations of different pharmaceuticals were found in alarmingly high concentrations in various parts of the globe, and it was also observed that the concentration of PhACs present in the water could be eventually related to the socio-economic conditions and climate of the region. Drinking water equivalent limit for each PhAC has been calculated and compared with the occurrence data from various continents. Since these compounds are recalcitrant towards conventional treatment methods, while advanced oxidation processes (AOPs) have shown better efficiency in degrading these PhACs. The performance of the AOPs have been evaluated based on percentage removal, time, and electrical energy consumed to degrade different classes of PhACs. Ozone based AOPs were found to be favorable because of their low treatment time, low cost, and high efficiency. However, complete degradation cannot be achieved by these processes, and various transformation products are formed, which may be more toxic than the parent compounds. The various transformation products formed from various PhACs during treatment have been highlighted. Significant stress has been given on the role of various process parameters, water matrix, oxidizing radicals, and the mechanism of degradation. Presence of organic compounds, nitrate, and phosphate usually hinders the degradation process, while chlorine and sulfate showed a positive effect. The role of individual oxidizing radicals, interfering ions, and pH demonstrated dissimilar effects on different groups of PhACs.

Design and development of a hybrid macrophyte assisted vermifilter for the treatment of dairy wastewater: A statistical and kinetic modelling approach

Global urbanization, exponential increase in population and sophisticated life style of the present generation are the major causes leading to a rapid increase in water demand in recent years. In order to nullify this rising water demand, it's high time to reuse domestic as well as industrial effluent after providing suitable chemical/biological treatment. Macrophyte filter incorporated with earthworm is identified as one of the most economic system for the treatment purpose in developing countries. However, very few literatures and technical information are available to scale up the design and its easy operation. This paper aims to develop a hybrid system and assess its performance for the purification of dairy wastewater. In the present study, two stage macrophyte assisted vermifilters (MAVFs) have been designed. The 1st stage encompassed a vertical flow (VF) unit, and the 2nd stage contained a horizontal flow (HF) unit. Both the units were inoculated with earthworm Eisenia fetida and were planted with Canna indica. Box-Behnken model was applied to design the system and study the effect of various parameters. It was observed that hybrid MAVF system removed a maximum of 83.2% COD and 57.3% TN at HLR 0.6 m/d and an active layer depth of 30 cm. Ammonification and nitrification typically occurred in the active layer (earthworm inoculated zone) of VF unit due to high activity of earthworms and its associated gut microbes, whereas HF unit facilitate denitrification process. Earthworm growth characteristics in the system were monitored, which is an imperative factor for the design of MAVF reactor. Kinetic modelling of 1st order, grau 2nd order and Stover-Kincannon model were performed and the Stover-Kincannon model showed high regression coefficient (COD, R² 0.9961 and TN, R² 0.9353) supporting its applicability as compared to the other models.