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The removal of trivalent chromium [Cr(III)] from tannery wastewater is necessary for health regulation compliance. In this work, two precipitating agents, namely, sodium hydroxide (NaOH) and calcium hydroxide [Ca(OH)2] were used to remove Cr(III) from Amatong Tannery wastewater by chemical precipitation. Wastewater characterization along with the most affecting parameters such as the effect of pH on Cr(III)) removal and sludge volume, average sludge volume and the settling time were investigated. The results show that optimum pH for Cr(III) removal by NaOH and Ca(OH)2 were found as 8.5 and 8.5-9.0, respectively, with supernatant Cr(III) concentration as 1.23 and 4.1 mg/L, respectively; the removal efficiency of NaOH was 99.94% and 99.8% for Ca(OH)2. At optimum pH, NaOH exhibited much sludge volume, whereas Ca(OH)2 displayed higher supernatant volume. NaOH: Ca(OH)2 volume ratio for sludge volume at optimum pH and average sludge volume were 1:1.24 and 1:1.8, respectively. [ABSTRACT FROM AUTHOR]

The facile, efficient, and straightforward preparation of electrode material for energy storage devices has drawn considerable interest for practical applications. In this study, we have synthesized the polyhedron Cu-doped ZnS (ZnS:Cu) structure on carbon cloth (CC) using a single-step glycol-assisted process. The highly interconnected polyhedron shaped ZnS:Cu functions as positive electrode material in an aqueous electrolyte for supercapacitor application. The ZnS:Cu polyhedron-like structures with higher electroactive sites and synergistic effect exhibited higher specific capacitance of 468 F g−1 at 1 Ag−1 and cycling stability of 890.5% after 5,000 cycles. The better electrochemical performance and higher cycling stability of ZnS:Cu can be dedicated to interconnected polyhedron-like structures, doping of Cu in ZnS, and binder-free electrode design. This underlines the potential of the Cu-doped ZnS-based supercapacitor for next-generation energy storage devices. [ABSTRACT FROM AUTHOR]