Water contaminated with arsenic is a worldwide problem. This review presents the arsenic contamination in groundwater, its sources, and possible health risk to humans. Groundwater pollution is the most common route of inorganic arsenic exposure in humans. Arsenic concentrations in different countries were analyzed and projected on a map. Because arsenic is widely spread throughout the Earth’s crust, it is present in trace amounts in practically all waterways. Harmful levels of this toxin have been identified in drinking water in some regions. For drinking purposes, the majority of people use groundwater; excess arsenic levels in groundwater have been linked to a variety of negative health impacts on people. Arsenic exposure is the world’s leading environmental cause of cancer. The main aim of this review is to summarize the effective technologies to remove arsenic from drinking water, such as ion exchange, coagulation/flocculation, and membrane technologies like ultra-filtration and electrodialysis, helping to deal with the adverse effects caused by arsenic exposure. All these technologies present different advantages and disadvantages. Electrocoagulation, adsorption, and phytoremediation are the most efficient and cost-effective technologies. The removal efficiencies of arsenic using these technologies and prospects were also included.

Heterogeneous catalyst prepared from Ailanthus altissima oil cake along with cadmium sulphide catalyst proved to be an efficient, cost-effective and sustainable source of biodiesel synthesis from Ailanthus altissima (Mill.) seed oil. Ailanthus altissima (Mill.) is a non-edible wild plant having significant oil content of 40%, being an ideal low cost and sustainable source of biodiesel production. After extraction of oil from the seeds, the remaining Ailanthus cake was treated through different techniques to be used as a novel heterogeneous catalyst. Free fatty acid content of the seeds was measured as 0.7%, which is very reasonable for effective trans-esterification process. The potassium hydroxide (KOH)-activated Ailanthus cake (KAC), calcined Ailanthus cake (CAC) and cadmium sulphide nanoparticles (CdS) were characterised with different techniques such as SEM at different magnifications, XRD and EDX. These catalysts were effectively utilised for biodiesel production owing to promising reusability, cost-effective and eco-friendly behaviour. For trans-esterification of Ailanthus altissima oil (AAO), the operating conditions on which maximum biodiesel yield obtained were 3:1 methanol to oil molar ratio, 0.5 wt.% catalyst concentration, 90 min reaction time, 60 °C and 600 rpm. The fuel properties of biodiesel obtained from Ailanthus altissima (Mill.) were also determined and analysed in detail. These properties, such as viscosity, density, pour point and cloud point, fall within the limits set by international standards of biodiesel.

The current study includes the preparation of titanium based nanoparticles for effective photo catalytic degradation of the second generation antibiotic Ofloxacin from the simulated water. The nanoparticles were synthesized by simple sol-gel method via Ti-isopropoxide as Ti precursor and calcined at 300, 350, 400, and 450 °C. The synthesized nanoparticles were characterized through Fourier transform infrared spectroscopy, photoluminescence spectroscopy, scanning electron microscopy and powder X-ray diffraction. Results of characterization study indicated the formation of anatase phase at low temperature. Degradation rate of 91, 87, 76, and 64% was achieved after 3 h of irradiations by TiO₂ calcined at 300, 350, 400, and 450 °C, respectively. Results indicated that by increasing calcination temperature, degradation rate of Ofloxacin was decreased due to increase in particle size and smaller surface area. Photo catalytic degradation of Ofloxacin proved that TiO₂ was an efficient catalyst for the removal of antibiotic from water samples.

This work reports the potential of novel non-edible seed oil of Lepidium perfoliatum Linn. (LSO) for accessing its potential to synthesize biodiesel using zirconium-modified montmorillonite clay catalyst. The newly synthesized zirconium-modified clay catalyst (ZrO-Mmt) was characterized using by X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDX), and Fourier transfer Infrared spectroscopy (FT-IR) spectroscopy. Response surface methodology (RSM) was used to optimize the Lepidium biodiesel (LBD) yield. Maximum biodiesel yield (88%) achieved under optimized reaction conditions were 1:15 oil: methanol, 3.5% catalyst amount at135°C for 4h respectively. Different techniques like FTIR, GC/MS, ¹H-NMR, and ¹³C-NMR were used for characterizing LBD. Additionally, major fuel properties of LBD for instance kinematic viscosity (4.10 mm²/s), density (0.8212kg/L), cloud point (−8 °C), flash point (74°C), and pour point (−9°C) agree well with the international biodiesel standards. Overall, Lepidium perfoliatum Linn. seed oil and ZrO-Mmt clay catalysts appear to be cheap, stable, and highly active contenders for the biodiesel industry.

The present study comprises the surfactant-based modified adsorbents as inorgano–organo composites for the removal of dyes. It was depicted that 0.05 g of modified clay could be efficiently used to adsorb >90% of dye (100 mg/L). The kinetic models (pseudo-first order, pseudo-second order, intraparticle diffusion model) and isothermal models (Langmuir, Freundlich, Temkin) were also studied to examine the adsorption mechanism. Pseudo second-order kinetic model and Langmuir isothermal model fitted well with adsorption of dyes. The thermodynamic ( $\Delta G°, \Delta H° \mathit{and} \Delta S°$) parameters were also studied and negative value of ( $\Delta G°)$ and positive value of ( $\Delta S°$) indicates the spontaneity of adsorption.