Solar Heterogenous Photocatalytic Degradation of Methylthionine Chloride on a Flat Plate Reactor: Effect of pH and H2O2 Addition

Abstract

Methylthionine chloride (MTC) is a compound with several applications both in the clinical and medical industries. Nevertheless, such compounds can become an environmental problem, as they are not properly treated by wastewater treatment plants. This objective of this work was to study MTC degradation in a flat plate reactor through solar photolysis and heterogeneous photocatalysis processes with TiO2 as a catalyst. In addition to the processes, three pH (3.5, 6.5, and 9) and the effect of H2O2 addition (no dose, 0.5, and 1 mM/L) were tested. The results show that acidic pH is the most appropriate for MTC degradation, which ranged between 56% and 68.7% for photolysis and between 76% and 86.7% in photocatalysis. The H2O2 addition resulted in lower degradation in all cases, leading the authors to conclude that the presence of peroxide actually hinders degradation in solar photolysis and photocatalysis processes. Statistical analysis showed that the constant rate reactions calculated for every process, under the same conditions of pH and H2O2 addition, are significantly different from one another, and the three factors considered for experimental design (process, pH, and H2O2) have a statistically significant effect on MTC degradation. The collector area per order confirmed higher efficiency for photocatalysis when compared to photolysis processes.

Arsenite to Arsenate Oxidation and Water Disinfection via Solar Heterogeneous Photocatalysis: A Kinetic and Statistical Approach

“…Experiments were carried out in the city of Durango (25.613238 • N, 103.435395 • W, 1900 m above sea level; Durango, Mexico), and they were performed during the summer, autumn, and winter seasons at solar noon. The city is located within the planet's sunbelt, which receives an average solar radiation in the range of 5.5 kWh/m 2 /day to 6.5 kWh/m 2 /day [40].…”

“…The collector area per order (A CO ) is the net area of irradiated photocatalyst needed, considering an average solar UV irradiance, to decrease a contaminant's concentration by one order of magnitude, within a unit of volume [40,62]. It can be calculated by Equation (4):…”

Photocatalytic Removal of Water Emerging Pollutants in an Optimized Packed Bed Photoreactor Using Solar Light

“…This way allows for the reusing of the catalytic materials from the treated effluent stream and the continuous operation, which are critical factors from an industrial point of view and scale-up [35,36]. Nevertheless, most of the current photocatalytic tests are only performed in batch photoreactors [37][38][39][40][41][42]. This experiment stage is the first step of catalyst testing.…”

Amoxicillin Degradation by TiO2 P25 Solar Heterogeneous Photocatalysis: Influence of pH and Oxidizing Agent H2O2 Addition

“…When radiation consisting of photons of wavelength lower or equal to 387 nm reaches the surface of the photocatalyst, an electron-hole pair (e − (CB) , h + (VB) ) is generated due to the promotion of electrons from valence band (VB) to conduction band (CB) [23], as shown in Equation (1):…”