From waste to value-added products: Evaluation of activated carbon generated from leather waste for supercapacitor applications.

Leather tanning operations create a large amount of solid and liquid waste from tanning, wherein Cr(III) compounds are used to produce wet blue leather. In this study, activated carbon (AC) generated from leather waste (LW) was evaluated for supercapacitor (SC) applications. AC was produced through carbonization at a temperature range of 700°C-900 °C, followed by chemical activation. The morphological characteristics of the AC samples revealed a certain degree of porosity and a maximum surface area of 381 m2 g-1. X-ray diffraction and EDX examination showed the existence of graphitic planes in the LW-derived AC. Raman, FT-IR, and XPS confirmed the defect nature and surface functional groups of the AC samples. A three-electrode approach was employed to assess the electrochemical characteristics of the AC samples. The supreme capacitance of a sample (LW700) at 1 A/g was 550 F g-1 (237 C g-1) in a 6 M KOH electrolyte. All the electrochemical results (CV, GCD, and Nyquist curves) demonstrated that the LW carbon possessed a high specific capacitance and electrochemical cycle constancy, and hence is appropriate for SC fabrication. These desirable capacitive performances enable solid leather waste-derived carbons as a source of new materials for low-cost energy storage supercapacitors. This work put forwards a new concept of 'waste to value-added products' that can be a helping hand for leather industries and its solid waste management disposal problems.

Carbon nitride/titania nanotubes composite for photocatalytic degradation of organics in water and sludge: Pre-treatment of sludge, anaerobic digestion and biogas production.

In this study, carbon nitride/titania nanotubes (C3N4/TiO2 NTs) composites were synthesized for the enhanced visible light mediated photocatalytic degradation and pre-treatment of wastewater sludge for enhanced biogas production. The co-existence of C3N4 and TiO2 NTs and visible light activity was confirmed by XRD, TEM, UV-visible and PL spectroscopy. The photocatalytic performance of TiO2 NTs with 2% of melamine (precursor of C3N4), enhanced the degradation of 2-chlorophenol (2-CP) (k = 0.0176 min-1), where 96.6% removal was achieved at optimum pH 7.0 and 2-CP concentration of 30 mg/L. On the other hand, the application of C3N4/TiO2 NTs for solubilization of the rigid structure of sludge by photocatalysis released the soluble organics showing an improvement in sCOD production (4587 mg/L). Subsequently, anaerobic digestion of solubilized sludge has improved the methane production (723.4 ml kg-1 VS) by 1.37 and 1.6 times compared to that in anaerobic digestion with photolytic and raw sludge, thus showing a promising applicability for biogas production from sludge and wastewater treatment.