Atomically-thin Schottky-like photo-electrocatalytic cross-flow membrane reactors for ultrafast remediation of persistent organic pollutants.

The remediation of persistent organic pollutants in surface and ground water represents a major environmental challenge worldwide. Conventional physico-chemical techniques do not efficiently remove such persistent organic pollutants and new remediation techniques are therefore required. Photo-electro catalytic membranes represent an emerging solution that can combine photocatalytic and electrocatalytic degradation of contaminants along with molecular sieving. Herein, macro-porous photo-electro catalytic membranes were prepared using conductive and porous stainless steel metal membranes decorated with nano coatings of semiconductor photocatalytic metal oxides (TiO2 and ZnO) via atomic layer deposition, producing highly conformal and stable coatings. The metal - semiconductor junction between the stainless steel membranes and photocatalysts provides Schottky - like characteristics to the coated membranes. The PEC membranes showed induced hydrophilicity from the nano-coatings and enhanced electro-chemical properties due to the Schottky junction. A high electron transfer rate was also induced in the coated membranes as the photocurrent efficiency increased by 4 times. The photo-electrocatalytic efficiency of the TiO2 and ZnO coated membranes were demonstrated in batch and cross flow filtration reactors for the degradation of persistent organic pollutant solution, offering increased degradation kinetic factors by 2.9 and 2.3 compared to photocatalysis and electrocatalysis, respectively. The recombination of photo-induced electron and hole pairs is mitigated during the photo-electrocatalytic process, resulting in an enhanced catalytic performance. The strategy offers outstanding perspectives to design stimuli-responsive membrane materials able to sieve and degrade simultaneously toxic contaminants towards greater process integration and self-cleaning operations.

Surfactant-modified titania for cadmium removal and textile effluent treatment together being environmentally safe for seed germination and growth of Vigna radiata.

The present work describes synthesis, detailed characterization, and application of bare and surfactant-modified titania nanomaterials (NMs) for various wastewater treatment applications as individual cases like cadmium (Cd) removal, methylene blue (MB) dye degradation, and treatment of real textile and dyeing industry effluent. These NMs are used as adsorbents and photocatalysts in an indegenously developed end-to-end treatment process and a photocatalytic reactor for treatment of textile wastewater. The used NMs are suitably filtered and recovered for reuse; however, still this work focusses on the extent of potential risk and environmental safety of these engineered NMs towards seed germination and plant growth, in the event they escape wastewater treatment plants and reach out to natural water bodies and soil systems, accumulate over a period of time, and comes in contact with plant species. For synthesis, sol-gel method was utilized; cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as cationic and anionic surfactants, respectively, to act as particle growth templates and improve surface morphology. Detailed characterization involved XRD (X-ray diffraction), FTIR (Fourier-transform Infrared Spectroscopy), SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy), EDX (Energy Dispersive X-ray analysis), and BET (Brunauer-Emmett-Teller) surface area analysis. Improved morphology and surface properties, from irregular shape in Bare TiO2 to spherical shape in surfactant-modified titania, led to enhanced Cd removal and MB dye degradation efficiency. Bare TiO2 was used for complete treatment of textile wastewater, which took 5 h in achieving water quality, which is safe for discharge and reuse as per norms of Central Pollution Control Board (CPCB), Govt. of India. Phytotoxicity studies of these NMs at a wide concentration range (0-1000 mg L-1) were undertaken towards Vigna radiata, and 500 mg L-1 concentration was found to be optimally safe for seed germination and plant growth.

Zinc peroxide nanomaterial as an adsorbent for removal of Congo red dye from waste water.

In the past decade, various natural byproducts, advanced metal oxide composites and photocatalysts have been reported for removal of dyes from water. Although these materials are useful for select applications, they have some limitations such as use at fixed temperature, ultra violet (UV) light and the need for sophisticated experimental set up. These materials can remove dyes up to a certain extent but require long time. To overcome these limitations, a promising adsorbent zinc peroxide (ZnO2) nanomaterial has been developed for the removal of Congo red (CR) dye from contaminated water. ZnO2 is highly efficient even in the absence of sunlight to remove CR from contaminated water upto the permissible limits set by the World Health Organization (WHO) and the United States- Environmental Protection Agency (US-EPA). The adsorbent has a specific property to adjust the pH of the test solution within 6.5-7.5 range irrespective of acidic or basic nature of water. The adsorption capacity of the material for CR dye was 208mgg-1 within 10min at 2-10pH range. The proposed material could be useful for the industries involved in water purification. The removal of CR has been confirmed by spectroscopic and microscopic techniques. The adsorption data followed a second order kinetics and Freundlich isotherm.