Efficient nitrate reduction in water using an integrated photocatalyst adsorbent based on chitosan-titanium dioxide nanocomposite

• Published in: Environmental science and pollution research international 2023-03, Vol.30 (13), p.38014-38030
• Main Authors: Venu Sreekala, Smitha, Parola, Athulya, Thayumani, Vimala, Puthenveedu Sadasivan Pillai, Harikumar, Thoppil Ramakrishnan, Resmi
• Format: Article
• Language: English
• Subjects: Adsorption; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Catalysis; Chitosan - chemistry; Earth and Environmental Science; Ecotoxicology; Environment; Environmental Chemistry; Environmental Health; Nanocomposites - chemistry; Nitrates - chemistry; Photoelectron Spectroscopy; Research Article; Titanium - chemistry; Waste Water Technology; Water - chemistry; Water Management; Water Pollutants, Chemical - chemistry; Water Pollution Control
• ISSN: 1614-7499; 1614-7499
• DOI: 10.1007/s11356-022-24895-5

Globally, there exists a huge concern on the increased discharge of nitrates to the natural water resources out of various anthropogenic activities as it causes serious environmental pollution and associated harmful effects. In the present work, sol–gel-derived functional nanocomposites based on silver (Ag) and nitrogen (N)-doped titanium dioxide (TiO 2 )-coated chitosan nanocomposites were successfully synthesized in the form of beads, and their application for the reduction of nitrates in water was studied. The synthesized nanocomposite beads were characterized for their structural, textural, and morphological features using X-ray diffraction analysis, Fourier transform infrared spectroscopy, UV–visible spectroscopy, BET surface area analysis, Scanning electron microscopy, Transmission electron microscopy, and X-ray photoelectron spectroscopy. A uniform coating of doped titania species on the chitosan porous structure was achieved through electrostatic interaction. Adsorption/photocatalytic reduction of nitrates was further carried out using functional nanocomposite beads by monitoring the nitrate concentration of the model contaminated water, in an adsorption study under dark condition and photocatalytic study under UV/sunlight for a definite time period. Drying conditions of the nanocomposite beads were found to have a significant effect on the adsorption cum photocatalytic efficiencies of the nanocomposite. The freeze-dried chitosan-titania nanocomposite beads containing 0.5 mol% Ag exhibited an adsorption efficiency of ~ 43.5% (under dark for 30 min) and photocatalytic reduction capability of ~ 95% (under sunlight for 2 h), whereas the oven dried beads of the same composition exhibits adsorption and photocatalytic efficiencies of 40% (under dark for 30 min) and 70% (under UV light for 2 h) respectively, towards the reduction of nitrate ions in an aqueous solution. Continuous flow adsorption cum photocatalytic study using the oven-dried nanocomposite beads was also carried out with the help of an experimental setup fabricated in-house and under varying experimental conditions such as flow rate, bed height, and concentration of feed solution. Nitrate reduction efficiency of 87.6% and an adsorption capacity of 7.9 mg g −1 were obtained for the nanocomposite beads in the continuous flow adsorption cum photocatalysis experiment for up to 8 h when using an inlet concentration of 100 ppm, bed height 12 cm, and flow rate 5.0 mL min −1 . A representative fixe