The water matrix plays a complex and significant role in photocatalytic degradation by influencing several factors, including dissolved anions and cations, the presence of natural organic matter, dissolved oxygen, suspended particles, turbidity, pH, and temperature. Optimizing photocatalytic processes for practical water treatment applications necessitates understanding these relationships. The efficiency and efficacy of photocatalytic water treatment systems in degrading organic contaminants can be enhanced by carefully considering and manipulating the water matrix. Based on literature published between 2000 and 2024, this review aims to comprehend the effects of contaminants and water quality on the photocatalytic degradation of organic pollutants. Researchers have employed various water matrices and reaction conditions to understand the interactions and impacts of different water matrix pollutants on photodegradation. The literature analysis revealed that when chloride and sulfate ions interact with reactive oxygen species and photocatalysts, their effects are predominantly inhibitory, thereby reducing the photocatalytic activity of the catalysts. Conversely, nitrate ions can exhibit an inhibitory effect under certain conditions by scavenging hydroxyl radicals while promoting photodegradation in other scenarios by generating more reactive oxygen species. The degree of inhibition varies according to the concentration of these factors.

This study presents an efficient way to degrade methylene blue (MB) present in water via photodegradation using H₂O₂ as an oxidant in the presence of UV irradiation and without the use of a catalyst. The reaction variables, employed to evaluate the performance of the photodegradation process using the UV/H₂O₂ system, were the amount of H₂O₂ in the reacting solution and the initial concentration of methylene blue. The degradation of methylene blue in the presence of H₂O₂ was not observed during agitation in darkness. The degradation time decreased as the H₂O₂ concentration increased after the ideal concentration was reached. At this stage, as it began to scavenge the generated hydroxyl radicals, the rate of degradation became inversely proportional to the concentration of H₂O₂. An increase in the quantities of MB and H₂O₂ improved the degradation efficiency because the oxidation process was aided by using the appropriate amount of H₂O₂ and an ideal length of UV light exposure. The experimental data obtained were well-fitted to zero-order reaction kinetics based on the high values of the correlation coefficient. It is believed that the OH radicals (OH^●) generated during the breakdown of H₂O₂ and the generated O₂^●− species attack the MB molecules and produce MB radicals (MB^●). These MB radicals further experience oxidation and convert to intermediates and finally to CO₂ and H₂O. The UV/H₂O₂ system proved to be quite efficient for the photodegradation of methylene blue without the use of any solid catalyst. This UV/H₂O₂ system can be employed in the degradation of other organic pollutants in industrial wastewater.