A review of novel green adsorbents as a sustainable alternative for the remediation of chromium (VI) from water environments

Construction of hierarchical nanostructured surface on an organic hybrid selenidostannate with light trapping effect to achieve sunlight-driven environmental remediation

Due to the low intensity of sunlight, it is a great challenge to realize highly efficient sunlight-driven photocatalysis. To maximize the utilization of sunlight, increasing the light capturing ability of photocatalysts is a prerequisite to attain high catalytic performances. Due to the multiple reflections of light in the hierarchical nanostructures, constructing hierarchical nanostructured surface should boost the sunlight capturing ability of a photocatalyst. Herein we used a surface oxidation etching method to construct a hierarchical nanostructure on the surface of an organic hybrid selenidostannate [Bmim]4[Sn9Se20], namely BTSe. After 24 hours of etching by ammonium persulfate, the surface of BTSe-O24 turned into a hierarchical nanostructure. FDTD simulation proved that the hierarchical nanostructure can effectively decline the loss of incident light and enhance light capturing ability of BTSe-O24. As a result, BTSe-O24 can completely reduce Cr(VI) (100 mg/L) in 8 min with a conversion rate of 750 mg/(g h) under sunlight. The catalytic performance of BTSe-O24 under sunlight is even better than those of most reported photocatalysts under high-power xenon lamps. More importantly, BTSe-O24 can maintain high photocatalytic efficiency in the whole daytime (from 8:00 to 16:00 in autumn and winter). Our research opens a new perspective on the design of sunlight-driven photocatalysts.

Entrapment behaviours of trivalent and hexavalent chromium from aqueous medium using edible alkali-derived activated carbon of Eichhornia crassipes (water hyacinth)

The study examines the adsorption capabilities of an environmentally friendly activated carbon derived from a novel activating agent, i.e., an edible alkali prepared from black gram plant ash, for the removal of Cr(III) and Cr(VI) ions from an aqueous environment. The results of the systematic research show impressive removal efficiencies of 95.12% for Cr(III) ions and 99.6% for Cr(VI) ions. The kinetics and equilibrium data of the adsorption process confirm to the pseudo-second-order kinetics and Freundlich isotherm model. The thermodynamic analysis reveals the adsorption process as feasible and spontaneous across the temperature range of 298-313 K. The mechanism entails electrostatic attraction and adsorption of Cr(III) and Cr(VI) ions on oppositely charged surfaces and the participation of oxygen-containing functional groups on WHAC-BGA surface in the reduction of Cr(VI) to Cr(III). This study provides valuable insights for optimizing strategies to combat chromium contamination in water sources, offering a sustainable solution with the potential for real-world application.

Efficiency of Ppy-PA-pani and Ppy-PA composite adsorbents in Chromium(VI) removal from aqueous solution

In this study, first time the combination of composites with Phytic acid (PA) as the organic binder cross-linker is reported. The novel use of PA with single and double conducting polymers (polypyrrole (Ppy) and polyaniline (Pani)) were tested against removal of Cr(VI) from wastewater. Characterizations (FE-SEM, EDX, FTIR, XRD, XPS) were performed to study the morphology and removal mechanism. The adsorption removal capability of Polypyrrole - Phytic Acid - Polyaniline (Ppy-PA-Pani) was deemed to be higher than Polypyrrole - Phytic Acid (Ppy-PA) due to the mere existence of Polyaniline as the extra polymer. The kinetics followed 2nd order with equilibration at 480 min, but Elovich model confirmed that chemisorption is followed. Langmuir isotherm model exhibited maximum adsorption capacity of 222.7-321.49 mg/g for Ppy-PA-Pani and 207.66-271.96 mg/g for Ppy-PA at 298K-318K with R2 values of 0.9934 and 0.9938 respectively. The adsorbents were reusable for 5 cycles of adsorption-desorption. The thermodynamic parameter, ΔH shows positive values confirmed the adsorption process was endothermic. From overall results, the removal mechanism is believed to be chemisorption through Cr(VI) reduction to Cr(III). The use of phytic acid (PA) as organic binder with combination of dual conducting polymer (Ppy-PA-Pani) was invigorating the adsorption efficiency than just single conducting polymer (Ppy-PA).