The challenges posed by water pollution have necessitated significant advancements in the development of sustainable technologies, particularly in addressing resilient pollutants that are resistant to conventional chemical and biological treatments. One of the pressing concerns on a global scale is the contamination of water bodies with pharmaceutical wastewater. Pharmaceutical drugs have become indispensable for human well-being and health, as evidenced by the substantial growth of the worldwide pharmaceutical market. In order to achieve the desired effects on humans or animals, pharmaceutical manufacturers are obligated to supply potent and durable pharmaceuticals. The recent COVID-19 pandemic serves as a compelling illustration of the reliance on drugs, as new anti-COVID-19 medications were specifically developed to combat the virus.

Due to their continuous release resulting from the growing consumption and disposal of human and veterinary medicines, pharmaceuticals belonging to various therapeutic classes are now recognized as micropollutants and emerging environmental contaminants. Examples of therapeutic classes are non-steroidal anti-inflammatory drugs, antibiotics, beta-blockers, antiepileptics blood lipid-lowering agents, antidepressants, hormones and antihistamines. The primary route through which these pharmaceuticals enter different water bodies is via wastewater treatment plants (WWTPs), although they can also originate from farms, households, industries, and hospitals. Since the first active pharmaceutical ingredient (API), clofibric acid was found in sewage effluent in Kansas City, USA in 1976, various other APIs have been detected in WWTPs and surface waters. Active pharmaceutical ingredients (APIs) are generally defined as complex molecules with different functionalities and physicochemical and biological properties. While pharmaceuticals are typically detected in the environment at concentrations ranging from picograms per liter (pg/L) to micrograms per liter (µg/L), there are instances where their levels can surpass milligrams per liter (mg/L). The presence of these pharmaceutical residues and metabolites has been linked to notable impacts on human health and aquatic organisms. Of particular concern is the presence of antibiotic-resistance genes and antibiotic-resistant bacteria, which are attributed to the extensive use of antibiotics and are considered significant pollutants.

The occurrence of refractory pharmaceutical compounds is undeniably a nerve-racking issue that needs to be tackled from the root by employing advanced but sustainable and cost and also energy-efficient treatment technologies. A typical conventional wastewater treatment which comprises a combination of physical, biological and chemical processes, involves high operating cost and energy, inefficient in completely eliminating persistent pollutants, often produce hazardous by-products and generate a large amount of solid wastes. Hence, Advanced oxidation processes (AOPs) are regarded as one of the most suitable destructive methods for the degradation of hazardous water pollutants and are also anticipated to be widely used water treatment technologies in the near future. AOPs which were initially proposed in the 1980s for drinking water treatment have been applied to pharmaceuticals wastewater treatment in recent years. AOPs involves the generation of reactive oxygen species (ROS) such as hydroxyl radicals, sulfate radicals, ozone molecule, and oxygen molecule in sufficient quantity to initiate water purification. In general, AOPs hold several exceptional advantages such as rapid reaction rates for most chemicals, and capable to degrade or oxidize multiple pharmaceutical contaminants non-selectively without any generating solid. Examples of AOPs are chemical oxidation processes (e.g. ultrasonic, ozonation, Fenton), photochemical oxidation processes (UV combined with ozonation, UV combined with hydrogen peroxide, photo-Fenton) and photocatalytic processes (UV combined with titanium dioxide, TiO2 photocatalysis).

Among various AOPs, TiO2 photocatalysis has received great attention for the purpose of pharmaceutical wastewater treatment. This is mainly due to its thermal stability, high photo-activity, low toxicity and good chemical stability. TiO2 photocatalysis is practically more efficient than conventional methods such as coagulation, precipitation and adsorption due to various reasons. This AOP method is able to gradually degrade the contaminant molecules without producing any residues of the original material and therefore reducing the cost of handling sludge disposal. At present, many researchers have investigated the performance of TiO2 photocatalysis for the treatment or removal of various pharmaceutical candidates from wastewater at a laboratory scale using artificial light sources (e.g. UV lights, visible lights, UV-LED lights, solar simulators etc) and pilot scale using various designs of photoreactors in the presence of solar irradiation or sunlight.