Review on Greywater Treatment and Dye Removal from Aqueous Solution by Ferrate (VI)

Integrated Adsorption-Photodegradation of Organic Pollutants by Carbon Xerogel/Titania Composites

Recent studies on the removal of pollutants via adsorption include the use of carbon-based adsorbents, due to their high porosity and large surface area; however, such materials lack photoactive properties. This study evaluates the synergistic effect of integrated mesoporous carbon xerogel (derived from resorcinol formaldehyde) and titanium dioxide (TiO₂) for combined adsorption and photodegradation application. The complex formed between carbon xerogel and TiO₂ phase was investigated through FTIR, proving the presence of a Ti-O-C chemical linkage. The physicochemical properties of the synthesised adsorbent-photocatalyst were probed using FESEM, BET analysis and UV-Vis analysis. The kinetics, equilibrium adsorption, effect of pH, and effect of adsorbent dosage were investigated. The expansion of the absorbance range to the visible range was verified, and the corresponding band gap evaluated. These properties enabled a visible light response when the system was exposed to visible light post adsorption. Hence, an assistive adsorption-photodegradation phenomenon was successfully executed. The adsorption performance exhibited 85% dye degradation which improved to 99% following photodegradation. Further experiments showed the reduction of microorganisms under visible light, where no microbial colonies were observed after treatment, indicating the potential application of these composite materials.

Decoration of alumina hollow fibers with zinc oxide: improvement of the photocatalytic system for methylene blue degradation

The photocatalytic degradation of methylene blue (MB) in aqueous solutions and under visible light was investigated with dispersed and supported zinc oxide (ZnO) as catalysts. The ZnO catalyst was successfully impregnated in asymmetric alumina hollow fibers by the simple vacuum-assisted dip-coating method. According to energy-dispersive analyses, the photocatalyst was homogenously distributed in the substrate. A strong correlation was observed between the initial dye concentration and the efficiency of the supported photocatalyst. For the initial MB concentration of 5 mg L^-1 and catalyst dosage of 1 g L^-1, the photocatalytic system with both dispersed and supported catalysts reached almost 100% of MB degradation. The photocatalytic process followed the pseudo-first-order kinetic model, and, for the initial MB concentration of 5 mg L^-1, the apparent constants were 0.05415 and 0.00642 min^-1 for suspended and supported catalysts, respectively. The treated MB solutions presented low phytotoxicity to the germination Lactuca sativa seeds with germination indexes greater than 80% after irrigation with the treated MB solutions. The produced supported ZnO catalyst showed suitable photocatalytic stability even after several reuse cycles.

Photocatalytic degradation of MB by TiO2: studies on recycle and reuse of photocatalyst and treated water for seed germination

Photocatalysis is an effective way for treatment of wastewater and degradation of dyes. It is important to assess the reusability of photocatalyst and treated water after the treatment process. In this study, the photocatalytic activity of TiO₂ (titanium dioxide) and TiO₂-TMAOH (titanium dioxide-tetramethylammonium hydroxide) was analyzed for degradation of methylene blue dye. Enhanced degradation of methylene blue is observed while treated with TiO₂-TMAOH with photodegradation efficiency (PDE) 80% within 20 min. A further study shows the reusability of TiO₂ for degradation of dye for six cycles with a decrease in photodegradation efficiency from 90% (cycle-1) to 50% (cycle-2). Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and cyclic voltammetry (CV) analysis were carried out to identify the functional groups in treated water, traces of titanium, and TMAOH, respectively. Seed germination of Vigna radiata using TiO₂- and TiO₂-TMAOH-treated water shows equivalent and consistent growth. Water quality analysis of treated water shows improved biochemical oxygen demand (BOD) level (1.5 mg L^-1), which is suitable for reusability of water for many applications. The outcomes suggest treated water can be used for irrigation and plantation purposes.

Chitosan Encapsulation of FerrateVI for Controlled Release to Water:Mechanistic Insights and Degradation of Organic Contaminant

Tetraoxy-anion of iron in +6 oxidation state (Fe^VIO₄²⁻, Fe^VI), commonly called ferrate, has shown tremendous potential as a green oxidative agent for decontaminating water and air. Encapsulation of solid potassium salt of ferrate (K₂FeO₄) circumvents the inherent drawbacks of the instability of ferrate under humid conditions. In the encapsulated strategy, controlled release without exposing the solid ferrate to the humid environment avoids self-decomposition of the oxidant by water in the air, and the ferrate is mostly used to decontaminate water efficiently. This study demonstrated the formulation of oxidative microcapsules with natural materials present in chitosan, whose release rate of the core material can be controlled by the type of intermediate hydrocarbon layer and the pH-dependent swelling of chitosan shell. The pH played a pivotal role in swelling chitosan shell and releasing the core oxidant. In a strong acidic solution, chitosan tended to swell quickly and release Fe^VI at a faster rate than under neutral conditions. Additionally, among the several long-chain hydrocarbon compounds, oleic acid exhibited the strongest “locking” effect when applied as the intermediate layer, giving rise to the slow release of Fe^VI. Coconut oil and mineral oil, in comparison, allowed Fe^VI to penetrate the layer within shorter lengths of time and showed comparable degrees of degradation of target contaminant, methylene orange, under ambient temperature and near-neutral conditions. These findings have practical ramifications for remediating environmental and industrial processes.