Nanosized titanium dioxide (TiO₂) nanoparticles were used for the photocatalytic reduction of hexavalent chromium in the presence of formic acid. The photoreduction of Cr(VI) in the absence of formic acid was quite slow. When formic acid was added in the chromium solution as the hole scavenger, a rapid photocatalytic reduction of Cr(VI) was observed, owing to the consumption of hole and the acceleration of the oxidation reaction. Furthermore, three commercial TiO₂ nanoparticles (AEROXIDE^® P25; Ishihara Sangyo ST-01; FUJIFILM Wako Pure Chemical Corp.) were evaluated for the photoactivity of reduction of Cr(VI).

Environmental analysis does not become properly meaningful unless follow the standard procedure in sampling, preserving and also in analysis. This study investigates different studies on surface and groundwater pollution and discusses their findings along with impacts on environment, human health and aquatic ecosystem demolition. Fresh water is a vital need for drinking, household, agricultural and industrial use. Fresh water availability is shrinking worldwide due to imprudent use. Abound availability of fresh water in Bangladesh is now polluting due to unwise dumping of industrial, household, agricultural and municipal wastes. Water body in urban arena is severely polluted rather than rural part. The over concentration of DO, BOD, COD, EC, TDS, Cr, Cd, Pb was observed in Dhaka region. The highest arsenic concentration was found in the ground water of Lakshimpur. The main sources of pollution in industrial cities are anthropogenic sources like untreated industrial effluent and municipal wastes whereas in rural part the main sources of pollution are agricultural and naturogenic. Transboundary impact also intensifies some river water pollution. Government approved the policies, ordinance, acts and laws however, due to lack of proper implementation and monitoring water pollution problem increasing day by day.

UV-light irradiated photocatalytic reduction of Cr(VI) to Cr(III) in aqueous solution using ZnFe₂O₄ nanoparticles in the presence of formic acid was reported. X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and UV- Vis diffuse reflectance spectroscopy (DRS) were employed to characterize the ZnFe₂O₄ nanoparticles. The photocatalytic activity of pure ZnFe₂O₄ under UV irradiation was significantly low. However, the Cr(VI) reduction efficiency on nano-sized ZnFe₂O₄ in the presence of 0.40% formic acid reached 95.4% within 4 hours. Herein, the effect of pH, photocatalyst amount, initial concentration of Cr(VI) and formic acid concentration on the photocatalytic reduction of Cr(VI) was investigated. The results indicated that the photocatalytic reduction of Cr(VI) decreased with increase the initial concentration of Cr(VI), photocatalyst dosage and pH. In the results, the reduction rate constant was declined from 0.017 min^-1 to 0.0023 min^-1 with increase of initial concentration of Cr(VI) from 5 mg ‧ L^-1 to 25 mg ‧ L^-1. However, the reduction rate constant sharply increased from 0.000075 min^-1 to 0.0127 min^-1 with the increase of formic acid concentration from 0.05% to 0.40%. The formic acid could capture the photo-generated holes, and eventually formate (HCOO^–) ions could be converted into carbon dioxide radicals (‧CO₂^‒). Because of more negative redox potential for ‧CO₂^‒ radicals, Cr(VI) species could easily be reduced to Cr(III) under UV irradiation. The pseudo first order kinetic reaction was confirmed for this reduction process. A tenable mechanism for the photocatalytic Cr(VI) reduction has also been demonstrated.