Catalytic and Photocatalytic Nitrate Reduction Over Pd-Cu Loaded Over Hybrid Materials of Multi-Walled Carbon Nanotubes and TiO2

Abstract

TiO2 and carbon nanotube-TiO2 hybrid materials synthesized by sol-gel and loaded with 1%Pd−1%Cu (%wt.) were tested in the catalytic and photocatalytic reduction of nitrate in water in the presence of CO2 (buffer) and H2 (reducing agent). Characterization of the catalysts was performed by UV-Vis and fluorescence spectroscopy, X-ray diffraction, temperature programed reduction, N2 adsorption, and electron microscopy. The presence of light produced a positive effect in the kinetics of nitrate removal. Higher selectivity toward nitrogen formation was observed under dark condition, while the photo-activated reactions showed higher selectivity for the production of ammonium. The hybrid catalyst containing 20 %wt. of carbon nanotubes shows the best compromise between activity and selectivity. A mechanism for the photocatalytic abatement of nitrate in water in the presence of the hybrid materials was proposed, based in the action of carbon nanotubes as light harvesters, dispersing media for TiO2 particles and as charge carrier facilitators.

Nitrate Catalytic Reduction over Bimetallic Catalysts: Catalyst Optimization

“…Moreover, N 2 selectivity increases for the supports that have a higher percentage of CNTs in their composition. Similar results were previously reported by Silva et al [28]. However, regarding nitrate conversion values, in this work, the highest conversion values were obtained by the catalysts with a lower amount of carbon nanotubes in their constitution (20 and 50%).…”

“…Thus, the noble metal has increased importance in reaction selectivity since good metal dispersion promoted by the N-doped support could be a key step for the N 2 selectivity registered for the 1% Pd-1% Cu/CNT (BM 4h)-N catalyst. It has been reported that Pd-Cu activity is higher when it is supported on carbon materials, instead of being supported on metal oxides such as TiO 2 , Al 2 O 3 , SiO 2 and ZrO 2 [28]. However, in this study, one of the supports that presented the best performance for nitrate removal was TiO 2 , reaching a nitrate conversion of 99% after 120 min of reaction.…”

“…However, this catalyst led to the formation of large concentrations of NH 4 + , around 6.7 mg/L, which corresponds to a selectivity of 76% after 300 min of reaction. Several studies have already reported this selectivity to NH 4 + formation as the biggest disadvantage of using TiO 2 as support and it is attributed to the strong hydrogenation-promoting properties of TiO 2 , causing over-reduction [26,28,48].…”

“…Nitrate anions can adsorb on the exposed acid sites of the support, in close contact with metal particles, and would be reduced by excess electrons generated in the support after reduction. Even though titania-supported catalysts are very active, their selectivity towards N 2 formation is very low, and ammonia is usually produced in high concentrations [26][27][28][29].…”

A New Paper-Based Microfluidic Device for Improved Detection of Nitrate in Water

“…Nitrate in water emanates from several different sources with large quantities coming from fertilizer or manure runoff, atmospheric deposition, agricultural sources, septic tanks, and wastewater treatment plants. Since nitrate is the most stable form of nitrogen in oxygenated environments, all other forms of nitrogen-containing compounds in water can also become sources for dissolved nitrate [ 23 , 24 ]. Drinking water with high levels of nitrate increases the risk of developing colorectal cancer, thyroid disease, and central nervous system birth defects [ 25 ].…”