INST researchers have developed a low-cost method for removal of toxic chromium from wastewater from industries such as leather tanning and electroplating by using “sunlight” as a catalyst in combination with microfluidic technology. Toxicity of hexavalent chromium is a serious concern and as per World Health Organization reports, the tolerable concentration of hexavalent and trivalent chromium in drinking water is limited to 0.05 mg/l and 5 mg/l respectively. Thus, it becomes imperative to convert this hexavalent form of chromium to trivalent form. Several chemical and physico-chemical measures, such as ion exchange, adsorption, and bacterial and chemical reduction are employed for removal of Cr(VI) but most of these techniques are expensive and have low Cr(VI) removal efficiency.
The research group led by Dr. Bhanu Prakash from the Institute of Nano Science and Technology (INST), Mohali, an autonomous institute of the Department of Science and Technology, has developed a novel technology for the removal of toxic Cr(VI) ions by using sunlight for the catalytic process in combination with microfluidic technology to convert the toxic hexavalent form of chromium to the less toxic trivalent form. For this, they used a process called continuous flow photoreduction and validated this process in wastewater using TiO2 nanoparticles with the help of smartphone based colorimetry technique.
The researchers began the process with the fabrication of microfluidic reactors and synthesis of nanocatalysts. Next, the nanocatalysts were immobilized on the micro-reactor base and flow experiments were performed. The conversion extent was monitored using changes in absorption through ultraviolet-visible (UV-Vis) spectroscopy. This was followed by evaluating the performance of the reactor on the fundamentals of the micro-reactor and long-term stability of the photocatalyst with respect to the number of cycles or volume processed.
The research work, published in the Journal of Chemical Engineering, proposes that the process has the potential for industrial translation by enhancing the throughput of the process. This is possible by setting up microfluidic reactors in a parallel approach (array) or by micro-texturing the bulk reactor surface to enhance the efficacy of the process after repeated use.