Hazardous chemicals like toxic organic dyes are very harmful to the environment and their removal is quite challenging. Therefore there is a necessity to develop techniques, which are environment friendly, cost-effective and easily available in nature for water purification and remediation. The present research work is focused on the development` and characterization of the ecofriendly semi-interpenetrating polymer network (semi-IPN) nanocomposite hydrogels composed of polyvinyl alcohol (PVA) and alginate (Alg) hydrogel beads incorporating natural bentonite (Bent) clay as a beneficial adsorbent for the removal of toxic methylene blue (MB) from aqueous solution. PVA−Alg/Bent nanocomposite hydrogel beads with different Bent content (0, 10, 20, and 30 wt%) were synthesized via external ionic gelation method. The designed porous and steady structure beads were characterized by the use of Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM). The performance of the beads as MB adsorbents was investigated by treating aqueous solutions in batch mode. The experimental results indicated that the incorporation of Bent (30 wt%) in the nanocomposite formulation sustained the porous structure, preserved water uptake, and increased MB removal efficiency by 230% compared to empty beads. Designed beads possessed higher affinity to MB at high pH 8, 30 °C, and fitted well to pseudo-second-order kinetic model with a high correlation coefficient. Moreover, the designed beads had good stability and reusability as they exhibited excellent removal efficiency (90%) after six consecutive adsorption-desorption cycles. The adsorption process was found be combination of both monolayer adsorption on homogeneous surface and multilayer adsorption on heterogeneous surface. The maximum adsorption capacity of the designed beads system as calculated by Langmuir isotherm was found to be 51.34 mg/g, which is in good agreement with the reported clay-related adsorbents. The designed semi-IPN PVA−Alg/Bent nanocomposite hydrogel beads demonstrated good adsorbent properties and could be potentially used for MB removal from polluted water.

Hydrogen is contemplated as a promising renewable source of energy as compared to the fast depleting fossil fuels. The splitting of water for the generation of hydrogen is a perspective approach to produce sustainable fuel. Titanium dioxide is the most commonly used catalyst, the performance of which depends upon its electronic surface structure, bandgap, and type of radiation. This review article summarizes the state of the art developments about the photocatalytic activity of titanium dioxide for hydrogen production from the splitting of water. Special attention has been devoted to the addition of sacrificial reagents, metal/non-metal doping ions, and composite semiconductors in titania for absorbing visible light and enhancing charge separation on a catalyst surface for efficient energy generation of hydrogen fuel from water splitting.

Globally, water contamination by heavy metals is a serious problem that affects the environment and human health. Adsorption is the most efficient way of water treatment for eliminating heavy metals. Various hydrogels have been prepared and used as adsorbents to remove heavy metals. By taking advantage of poly(vinyl alcohol) (PVA), chitosan (CS), cellulose (CE), and the process for physical crosslinking, we propose a simple method to prepare a PVA-CS/CE composite hydrogel adsorbent for the removal of Pb(II), Cd(II), Zn(II) and Co(II) from water. Structural analyses of the adsorbent were examined by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis, and X-ray diffraction (XRD). PVA-CS/CE hydrogel beads had a good spherical shape together with a robust structure and suitable functional groups for the adsorption of heavy metals. The effects of adsorption parameters such as pH, contact time, adsorbent dose, initial concentration of metal ions, and temperature on the adsorption capacity of PVA-CS/CE adsorbent were studied. The adsorption characteristics of PVA-CS/CE for heavy metals may be completely explained by pseudo-second-order adsorption and the Langmuir adsorption model. The removal efficiency of PVA-CS/CE adsorbent for Pb(II), Cd(II), Zn(II), and Co(II) was 99, 95, 92, and 84%, respectively, within 60 min. The heavy metal’s hydrated ionic radius may be crucial in determining the adsorption preference. After five consecutive adsorption–desorption cycles, the removal efficiency remained over 80%. As a result, the outstanding adsorption-desorption properties of PVA-CS/CE can potentially be extended to industrial wastewater for heavy metal ion removal.

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Metal ions contamination is the leading cause of many health and environmental problems. In order to rectify and remediate the environment from metal ions contamination, simple, efficient and easy to fabricate sensors for the onsite detection of metals ions is obligatory. However, devising a practically applicable sensor that could be compatible to the environment which contains a plethora of other ions than the target metal ions, is very challenging. In this work we report a highly sensitive and selective yet simple and greener electrode for copper ions detection by modifying GCE with amino acid-L-tryptophan. The modifier brings about increase in active surface area of the GCE and effectively binds to the metal ions through the process of chelation utilizing its amino and carboxylic acid functional groups. Cyclic voltammetry (CV), square wave voltammetry (SWV) and square wave anodic stripping voltammetry (SWASV) along with electrochemical impedance spectroscopy (EIS) was conducted to investigate the surface of the electrode and its sensitivity towards detection of Cu 1+ and Cu 2+ ions. A number of experimental parameters such as pH, supporting electrolyte, concentration of the modifier, accumulation time and deposition potential were investigated to achieve best response of the metal ions towards the modified electrode. The designed sensor exhibited excellent electrocatalytic activity and sensitivity towards Cu 1+ ions even in the presence of 5-fold higher concentration of different interferents. The LOD (Limit of detection) of 3.13 pM as determined by the calibration curve was found to be much lower than permissible values suggested by the WHO (World Health Organization) and US EPA (Environmental Protection Agency). % age recoveries as estimated from real water samples was found to be within 3% RSD value and proved the validity of the proposed methodology for the designed sensor. Computational studies were carried out using hyperchem 7.5 software with semi empirical PM3 method. The negative value of binding energy of the merged molecule i.e., −3024.181 kcal mol −1 point towards significant interactions between L-tryptophan and Cu 2+ ions which is evident from the change in physicochemical properties upon merging of L-tryptophan with Cu 2+ ions. Our computational studies agree well with the experimental results.