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.

Hollow Polyaniline Microsphere/MnO2/Fe3O4 Nanocomposites in Adsorptive Removal of Toxic Dyes from Contaminated Water.

Dyes are considered as recalcitrant compounds and are not easily removed through conventional water treatment processes. The present study demonstrated the fabrication of polyaniline hollow microsphere (PNHM)/MnO2/Fe3O4 composites by in situ deposition of MnO2 and Fe3O4 nanoparticles on the surface of PNHM. The physicochemical characteristics and adsorption behavior of the prepared PNHM/MnO2/Fe3O4 composites towards the removal of toxic methyl green (MG) and Congo red (CR) dyes have been investigated. The characterization study revealed the successful synthesis of the prepared PNHM/MnO2/Fe3O4 adsorbent with a high Brunauer-Emmett-Teller (BET) surface area of 191.79 m2/g. The batch adsorption study showed about 88 and 98% adsorption efficiencies for MG and CR dyes, respectively, at an optimum dose of 1 g/L of PNHM/MnO2/Fe3O4 at pH ∼6.75 at room temperature (303 ± 3 K). The adsorption phenomena of MG and CR dyes were well described by the Elovich and pseudo-second-order kinetics, respectively, and Freundlich isotherm model. The thermodynamics study shows that the adsorption reactions were endothermic and spontaneous in nature. The maximum adsorption capacity (Qmax) for MG and CR dyes was observed as 1142.13 and 599.49 mg/g, respectively. The responsible adsorption mechanisms involved in dye removal were electrostatic interaction, ion exchange, and the formation of the covalent bonds. The coexisting ion study revealed that the presence of phosphate co-ion considerably reduced the CR dye removal efficiency. However, the desorption-regeneration study demonstrated the successful reuse of the spent PNHM/MnO2/Fe3O4 material for the adsorption of MG and CR dyes for several cycles. Given the aforementioned findings, the PNHM/MnO2/Fe3O4 nanocomposites could be considered as a promising adsorbent for the remediation of dye-contaminated water.

Development of a schwarzite-based moving bed 3D printed water treatment system for nanoplastic remediation.

The impact of micro and nanoplastic debris on our aquatic ecosystem is among the most prominent environmental challenges we face today. In addition, nanoplastics create significant concern for environmentalists because of their toxicity and difficulty in separation and removal. Here we report the development of a 3D printed moving bed water filter (M-3DPWF), which can perform as an efficient nanoplastic scavenger. The enhanced separation of the nanoplastics happens due to the creation of a charged filter material that traps the more surface charged nanoparticles selectively. Synthetic contaminated water from polycarbonate waste has been tested with the filter, and enhanced nanoplastic removal has been achieved. The proposed filtration mechanism of surface-charge based water cleaning is further validated using density function theory (semi-empirical) based simulation. The filter has also shown good structural and mechanical stability in both static and dynamic water conditions. The field suitability of the novel treatment system has also been confirmed using water from various sources, such as sea, river, and pond. Our results suggest that the newly developed water filter can be used for the removal of floating nanoparticles in water as a robust advanced treatment system.

Lanthanum ions decorated 2-dimensional g-C3N4 for ciprofloxacin photodegradation.

The low band gap energy and high surface area two-dimensional materials allow it to tune its basic properties using surface decoration. Here, La3+ are decorated on two-dimensional graphitic carbon nitride using a simple and easily scalable chemisorption process with an adsorption capacity of 657.32 mg g-1. In the X-ray diffraction (XRD) study, the positive slope of the W-H plot elucidates the tensile strain generation (0.103) in La3+ ions decorated 2D-g-C3N4 (La3+-2D-g-C3N4). The high-resolution transmission electron microscope (HR-TEM) study and the higher ID/IG ratio (0.82) in the Raman spectroscopy study confirm the more defects intensification in La3+-2D-g-C3N4. The reduction in band gap energy for La3+-2D-g-C3N4 (from 2.83 eV to 2.21 eV) has shown a good correspondence with the band structures study as obtained from the DFT study. In the DFT study, the significant contributions of N atoms in charge transfer validate the N 1s findings from the X-ray photoelectron spectroscopy (XPS) study for La3+-2D-g-C3N4. La3+-2D-g-C3N4 shows the photodegradation efficiency (93%) of ciprofloxacin under UV irradiation, which is superior to pristine 2D-g-C3N4 (82%) as well as other g-C3N4 based nanocatalysts. Also, La3+ decoration results in enhancement (32.3%) in photodegradation kinetics rate. The degradation and kinetics studies in the presence of different scavengers ensure that the O2- and OH- radicals are mostly responsible for the ciprofloxacin photodegradation. The Liquid chromatographic-mass spectroscopy and the high-performance liquid chromatography studies confirm the photodegradation. The reusability of La3+-2D-g-C3N4 is tested up to the fifth cycle. FTIR and UV-visible absorption spectroscopy confirm the stability of the used photocatalyst.

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.

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.

Effect of bioflocculants on the coagulation activity of alum for removal of trihalomethane precursors from low turbid water.

Reactivity of chlorine towards hydrophobic groups present in natural organic matter (NOM) provokes the formation of carcinogenic disinfection byproducts such as trihalomethanes in chlorinated water. The present study aimed to investigate the variations in coagulant activity of alum using two different bioflocculants (coagulant aid) namely, Moringa oleifera and Cyamopsistetragonoloba for the removal of hydrophobic fractions of NOM and subsequent chlorine consumption by treated water. Effect of dual coagulants on trihalomethane surrogate parameters such as total organic carbon, dissolved organic carbon, UV absorbing materials and prominent hydrophobic species such as phenolic groups along with aromatic chromophores, polyhydroxy aromatic moiety have also been studied. The concept of differential spectroscopy and absorbance slope index has been employed to understand the combined effects of alum-bioflocculants on the reactivity of NOM with chlorine. Our result shows that the combination of alum and C. tetragonoloba is more efficient for reducing trihalomethane surrogates from chlorinated water as compared to M. oleifera. C. tetragonoloba elicited synchronized effects of sweep coagulation and particle bridging-adsorption which eventually facilitated efficient removal of hydrophobic fractions of NOM. The variation in the mechanistic approach of bioflocculants was due to the presence of cationic charge on M. oleifera and adhesive property of C. tetragonoloba.