THE ENHANCED PHOTOCATALYTIC PROPERTIES OF SILVER PHOSPHATE SYNTHESIZED UNDER MANGOSTEEN PEEL EXTRACT SOLUTION

The synthesis of silver phosphate (Ag3PO4) photocatalyst has been widely developed for organic pollutant degradation. However, the large particle of this photocatalyst limits the photocatalytic activity. The smaller particle size of the Ag3PO4 photocatalyst was successfully prepared using the starting material of AgNO3 and Na2HPO4.12H2O under mangosteen peel extract solution. The starting materials were dissolved in mangosteen peel extract solutions prepared at the concentration of 1% (w/v). The reaction of silver nitrate and phosphate solution was conducted at room temperature. The samples of pristine Ag3PO4 and Ag3PO4 prepared under mangosteen peel extract were studied using XRD, DRS, SEM, BET, and FTIR. All photocatalytic activities were evaluated using Rhodamine B photooxidation under blue light irradiation (LED, 3 Watt). The results showed that the mangosteen peel extract significantly decreased the particle size, lowered the bandgap energy from 2.12 to 2.00 eV, and increased the crystallinity of Ag3PO4. The interaction of xanthones from mangosteen peel extract solution with silver ion might affect the growth particle of Ag3PO4, and inhibit the agglomeration leading to small particle size, more uniform distribution, high crystallinity, and low bandgap energy. These properties enhanced the photocatalytic activity up to 2.9 times higher compared to the sample without the treatment of mangosteen peel extract.

Valorization of Brewery Wastes for the Synthesis of Silver Nanocomposites Containing Orthophosphate

Brewery wastes from stage 5 (Wort precipitate: BW5) and stage 7 (Brewer’s spent yeast: BW7) were valorized for the synthesis of silver phosphate nanocomposites. Nanoparticles were synthesized by converting silver salt in the presence of brewery wastes at different temperatures (25, 50, and 80 °C) and times (10, 30, and 120 min). Unexpectedly, BW7 yielded Ag3PO4 nanoparticles with minor contents of AgCl and Ag metal (Agmet). Contrastingly, BW5 produced AgCl nanoparticles with minor amounts of Ag3PO4 and Agmet. Nanocomposites with different component ratios were obtained by simply varying the synthesis temperature and time. The morphology of the nanocomposites contained ball-like structures representative of Ag3PO4 and stacked layers and fused particles representing AgCl and Agmet. The capping on the nanoparticles contained organic groups from the brewery by-products, and the surface overlayer had a rich chemical composition. The organic overlayers on BW7 nanocomposites were thinner than those on BW5 nanocomposites. Notably, the nanocomposites exhibited high antibacterial activity against Escherichia coli ATCC 25922. The antibacterial activity was higher for BW7 nanocomposites due to a larger silver phosphate content in the composition and a thin organic overlayer. The growth of Agmet in the structure adversely affected the antimicrobial property of the nanocomposites.

ZnO/Ag3PO4 and ZnO–Malachite as Effective Photocatalysts for the Removal of Enteropathogenic Bacteria, Dyestuffs, and Heavy Metals from Municipal and Industrial Wastewater

Different composites based on ZnO/Ag3PO4 and ZnO–malachite (Cu2(OH)2CO3) were synthesized in order to determine their effectiveness in the treatment of municipal and industrial wastewaters (mainly polluted by enteropathogenic bacteria, dyes, and heavy metals). The addition of Ag3PO4 and malachite did not significantly modify the physicochemical properties of ZnO; however, the optical properties of this oxide were modified as a result of its coupling with the modifiers. The modification of ZnO led to an improvement in its effectiveness in the treatment of municipal and industrial wastewater. In general, the amount of malachite or silver phosphate and the effluent to be treated were the determining factors in the effectiveness of the wastewater treatment. The highest degree of elimination of bacteria from municipal wastewater and discoloration of textile staining wastewater were achieved by using ZnO/Ag3PO4 (5%), but an increase in the phosphate content had a detrimental effect on the treatment. Likewise, the highest Fe and Cu photoreduction from coal mining wastewater was observed by using ZnO–malachite (2.5%) and ZnO/Ag3PO4 (10%), respectively. Some of the results of this work were presented at the fourth Congreso Colombiano de Procesos Avanzados de Oxidación (4CCPAOx).