Desenvolvimento e aplicação de compósitos à base de TiO2 e biomassas carbonáceas para remoção de poluentes orgânicos em água

Abstract

The association of materials with adsorption and photocatalytic properties has been shown to be particularly efficient for the removal and degradation of toxic and non-biodegradable molecules in aqueous matrices. Photocatalytic semiconductors doped with carbonaceous materials presents desirable properties with larger contact surface and high adsorption performance, bringing the pollutant closer to the catalyst, in addition to the possibility of expanding the absorption of solar spectrum radiation. Furthermore, biomass from agricultural waste can reduce the composite production costs, making them more sustainable. In this context, the present work resulted in a systematic review with 107 selected articles (832 entries and 41 variables). The synthesis of biomass-based composites (BCPs) and their removal efficiency towards organic and inorganic pollutants in water revealed an average efficiency removal and photocatalytic degradation rate of target pollutants by BCPs of 77.5 ± 21.5% and 0.064 ± 0.174 min-1, respectively. As evidenced from principal component analysis (PCA), the BCPs synthesis method, calcination temperature, surface area, and porosity affected the morphological and structural characteristics of BCPs as well as their photocatalytic activity. Experimental tests were carried out using two methodologies (impregnation and sol-gel) and two calcination temperatures (400 and 600 °C), producing composites formed by Ti and carbonaceous biomass (biochars and raw biomass coconut shells). The composite synthesized by the sol-gel method and calcination temperature of 400 °C with Ti and coconut biomass (TTiP-C400) showed superior performance in the preliminary MB dye removal tests (91.4%) compared to commercial P25-TiO2 (72%). Thus, the TTiP-C composite was synthesized by varying the Ti:coconut ratio (0:100; 25:75; 50:50; 75:25 and 100:0), the temperature and type of calcination (400 and 600 ° C, with or without stainless steel case, respectively). The adsorption and photocatalytic capabilities of the composites were evaluated for methylene blue dye (MB) removal and the micropollutants bisphenol S, carbamazepine, clonazepam and perfluorooctanoic acid (BPS, CBZ, CZP and PFOA, respectively. Among the materials without stainless steel boxes (BCPs), the best result was BCP400 50:50, a composite calcined at 400ºC and a 50:50 ratio (Ti:coconut). Through experimental design (DoE) focusing on the variables: pH, catalyst concentration and radiation intensity, BCP400 50:50 removed 91% of MB in 30 min, while commercial P25-TiO2 and TiO2 synthesized without coconut (T400) removed 51.2% and 8.5%, respectively, in 30min. The BCP400 50:50 was also subjected to three recycling tests, showing lower pollutant removal on the third cycle, probably due to pore saturation. Regarding composites produced in stainless steel boxes (BCP-I), the best composite (BCP600 25:75-I, calcined at 600ºC and Ti:coconut ratio of 25:75) was submitted to the DoE focusing on the variables: pH, temperature and adsorbate/adsorbent ratio. From the optimized variables, 99.2%, 98.7%, 99.3% and 2% of BPS, CBZ, CZP and PFOA were removed from ultrapure water, and 89.5%, 68.7%, 57.3% and 8.6% of BPS, CBZ, CZP and PFOA were removed from real effluent, respectively. The selected materials were characterized by X-ray diffractometry, FTIR, BET method, SEM and pHpzc. According to DR-X, the indexation of BCP400 50:50 and BCP600-25:75 occurred with the Potassium Titanate and Potassium Magnesium Titanium Oxide phases, respectively. The results suggested that the addition of KOH during the synthesis could inhibit the phase transformation of TiO2. The composites calcined in a stainless-steel box and at 600 ºC showed a greater specific surface area and greater pore volume, resulting in better-performing composites. Considering the mild pyrolysis conditions applied and the carbonaceous material from agricultural waste, the synthesized composites may have a significant advantage in production cost compared to available literature. The results revealed that adsorption is the predominant factor in the removal of micropollutants, however the role of photocatalysis must be explored as an additive to the degradation of these contaminants.