Sunlight active PSf/TiO 2 hybrid membrane for elimination of chromium

Industrial steel waste recovery pathway: Production of innovative supported catalyst and its application on hexavalent chromium reduction studies

Mill scale is the metallurgical waste produced by the rolling mill in the steel hot rolling process. This hazardous waste is mainly composed of oxide iron, such as hematite, magnetite and wustite. It may have a different and alternative final destination by becoming a catalyst for wastewater treatment. In this work, the catalytic potential of mill scale (MS) from a steel plant was evaluated for hexavalent chromium reduction from synthetic and real matrices under slurry conditions (MS particles dispersed in the solution) or immobilized in Raschig rings. Experiments were conducted in an annular photoreactor irradiated by UVA light. Raschig rings were coated with MS by electrostatic link with polyethylene-grafted-maleic anhydride copolymer (PEGMA) film, and further packed in the annular zone of the UV photoreactor. SEM, XRD and FTIR analysis showed a homogeneous film of MS firmly attached on Raschig rings surface. In this way, the iron-rich industrial steel waste acted as both source of iron and photocatalyst, allowing the reduction of Cr(VI) to Cr(III) in the bulk solution and MS surface, respectively, in the presence of tartaric acid as hole and hydroxyl scavenger and Fe-complexing agent. The Raschig rings (248 g) coated with MS (23 g) achieved total Cr(VI) reduction (below detection limit) after 45 min of reaction (k = 2.0 × 10^-2 mg L^-1 min^{- 1}) under UVA radiation, considering the following initial conditions: [Cr(VI)]₀ = 10 mg L^-1, [tartaric acid]₀/[Cr(VI)]₀ molar ratio = 6:1, pH = 3.0, T = 25 °C. The same system was tested for the treatment of a real effluent from a galvanic industry containing 6 mg L^-1 of Cr(VI). Using the same tartaric acid/Cr(VI) molar ratio (6:1) and pH 3.0, the Cr(VI) present in the effluent was totally reduced (below detection limit) in 360 min (k = 1.93 × 10^-2 mg L^{- 1} min^{- 1}), showing similar kinetic behavior as the process with the synthetic matrix. In all experiments, the concentrations of dissolved iron (Fe(II) and Fe_(total)) were below the disposal limit established by Brazilian legislation, and total chromium removal was achieved by Cr(III) precipitation after the photocatalytic reaction.

TiO2-based catalysts for photocatalytic reduction of aqueous oxyanions: State-of-the-art and future prospects

Nowadays, an increasing discharge of oxyanions to the natural environment has been attracting worldwide attention. TiO₂-based photocatalysis is regarded as one of the most promising technologies for the conversion of toxic oxyanions (such as chromate, nitrate, nitrite, bromate, perchlorate and selenate) to harmless and/or less toxic substances in contaminated waters. Various types of TiO₂-based catalysts have been developed, and each of them exhibits its own advantages in catalytic reduction of oxyanions. However, the application of these nanostructured TiO₂ in real water bodies remains a challenge, with limitations associated with sunlight harvesting abilities, production costs, reuse stability and exposure risks. Herein, we aim to present a critical review on reported TiO₂-based photocatalytic reduction of aqueous oxyanions, provide a comprehensive understanding of the possible reaction pathways of formed active species, and evaluate the reduction performance of different types of TiO₂-based catalysts. In addition, the impact of operating parameters (such as solution pH, temperature, dissolved oxygen and coexisting substances) on catalytic reduction performance is discussed. Furthermore, the perspectives of TiO₂-based photocatalytic reduction of oxyanions are also proposed.

Adsorptive nanocomposite membranes for heavy metal remediation: Recent progresses and challenges

Heavy metal contamination in aqueous system has attracted global attention due to the toxicity and carcinogenicity effects towards living bodies. Among available removal techniques, adsorptive removal by nanosized materials such as metal oxide, metal organic frameworks, zeolite and carbon-based materials has attracted much attention due to the large active surface area, large number of functional groups, high chemical and thermal stability which led to outstanding adsorption performance. However, the usage of nanosized materials is restricted by the difficulty in separating the spent adsorbent from aqueous solution. The shift towards the use of adsorptive composite membrane for heavy metal ions removal has attracted much attention due to the synergistic properties of adsorption and filtration approaches in a same chamber. Thus, this review critically discusses the development of nanoadsorbents and adsorptive nanocomposite membranes for heavy metal removal over the last decade. The adsorption mechanism of heavy metal ions by the advanced nanoadsorbents is also discussed using kinetic and isotherm models. The challenges and future prospect of adsorptive membrane technology for heavy metal removal is presented at the end of this review.

Nonionic Glycolipids for Chromium Flotation- and Emulsion (W/O and O/W)-Based Bioactive Release

Biosourced surfactants are endeavored as a green alternative to biosurfactants and petrochemical surfactants having industrial utilization. Nine glycolipids with headgroup and chain length variation were derived from renewable resources like vegetable oils, carbohydrates, and amino acids. The concentration-dependent interfacial activity, foamability, wetting power, emulsification power, and solubilization capacities of glycolipids were investigated to provide a structure-activity relationship. Later, the metal flotation and emulsification experiments were performed. In general, for metal flotation, the surfactant should contain a hydrophobic tail, hydrophilic head, and chelating function. In the present investigation, it was observed that the headgroup of a glycolipid can serve as a hydrophilic head as well as perform a chelating function. Moreover, heat energy generated from the sunlight was utilized for metal flotation. Additionally, these glycolipids are capable to form stable sunflower oil-water (W/O and O/W) emulsions. The mechanical and thermal stabilities and hydrophobic chain length dependency of the prepared emulsions at different water volume fractions are explored. Furthermore, encapsulation and release of water-soluble (riboflavin and l-ascorbic acid) and oil-soluble (curcumin and α-tocopherol) bioactives in glycolipid emulsions were monitored. Thus, glycolipids under investigation had shown the possibility for pretreatment of chromium-containing wastewaters and bioactive-loaded emulsions toward the controlled release.

Titania nanowires coated PEI/P25 membranes for photocatalytic and ultrafiltration applications

Bulk compositing and surface functionalization are combined to achieve a polymeric membrane that is covered with TiO₂ nanowires, which possesses multi-functions of photodegradation, separation and self-cleaning.