Photocatalytic degradation of Pharmaceutical Compounds in Wastewater using Doped TiO2-SiO2 Photocatalyst

Abstract

India, a developing country, has surpassed the United States as the world's third largest producer of pharmaceutical drugs. The consumption of pharmaceuticals and personal care products (PPCPs) have increased dramatically in recent years. The concentration of PPCPs in the environment is typically extremely low, ranging from ngL-1 to gL-1 . Toxic nature of these substances and persistence in the environment have sparked widespread concern among societies and regulatory bodies around the world. Advanced Oxidation Processes (AOPs) such as photocatalysis have gained widespread popularity among researchers because of their ability to treat a wide range of pollutants. Pharmaceuticals have been detected in ground water, surface water, ocean, sediments, and soil. The detected compounds included antibiotics, antihistamines, anticonvulsants, painkillers, hormones, cytostatic drugs, lipid regulators, beta-blockers, and X-ray contrast media that are potentially harmful to the living being. According to present status of COVID-19 coronavirus, various antibiotics have sparked as potential COVID-19 treatment options in the year 2020. The huge demand and consumption of DOX and OFL, its incomplete metabolism and complex behavior in the atmosphere are causing a great ecological issue, which needs to be solved. In this regard, researchers have chosen Advanced oxidation processes (AOPs), which are

extremely promising methods for the treatment of contaminated wastewaters containing non- biodegradable organic pollutants.Titanium dioxide has been established as the most active

photocatalyst for the breakdown of organic molecules among numerous semiconductor materials. Because of its high efficiency, low cost, chemical, and physical stability, broad availability, and noncorrosive nature, Undoubtedly, TiO2 photocatalysis has established its reputation in the field of advanced wastewater treatment, but recombination of electrons and holes has always been a matter of concern when considering its commercial applications. High band gap energy (3.2 eV) enables TiO2 to absorb only UV light and limits its solar light application. Unfortunately, low surface area, aggregation and the difficulty in product recovery often limit its practical application. To overcome these limitations, many surface modification methods have been conceived. TiO2- SiO2 oxides have been widely employed as photocatalysts, displaying outstanding efficiency in

the removal of highly hazardous and non-biodegradable contaminants such as dyes, phenols, and benzenes from wastewater . TiO2 modification using SiO2 alone is insufficient to maximise TiO2 use in a solar light powered wastewater treatment process. As a result, in order to directly utilise the energy from sunlight, the third material must have a low band-gap energy (Eg < 3). The absorption edge of TiO2-SiO2 was roughly 400 nm, but doping techniques elevate the activity of nano-doped TiO2 from the UV region to the visible light region. The development of novel catalysts with high-efficiency photocatalytic performance under solar light is therefore of great significance for removal of the pharmaceutical compounds and further improve the pilot photocatalytic performance. In the present study, best efforts have been made to overcome these hurdles by doping and codoping TiO2-SiO2 photocatalyst with iron and copper metal ions. This will help in the advancement of ongoing efforts to prepare modified photocatalysts to enhance their solar light activity. This research proposes a water purification strategy that is efficient, clean, and recyclable for the removal of antibiotic contaminants. The main focus was to degrade different pharmaceutical drugs like Doxycycline (DOX), Amoxicillin (AMX), Ofloxacin (OFLX), and Cetirizine using the TiO2-SiO2 based photocatalysis. The synthesised photocatalyst was characterised for its physical and chemical properties using different characterization techniques such as, XRD, FTIR, DRS, FESEM, TEM, RS, and BET. The photocatalytic experiments were investigated under visible, UV, and solar light (on sunny days). The prepared undoped, doped, and codoped TiO2-SiO2 nano photocatalyst were used in the photocatalytic degradation of AMX, CTZ, DOX, and OFLX. Photocatalytic experiments were performed in a shallow pond slurry reactor made of borosilicate glass under continuous magnetic stirring. The concentration of antibiotics were measured continuously using a UV-Vis spectrophotometer. Effect of various parameters like time, solution pH, catalyst loading, dopant concentration, intensity of light and A/V ratio were studied on the degradation efficiency of antibiotics. The concentration of OH• radicals was determined, as well as its role in the photocatalytic degradation of drugs. Moreover, to check the durability of the photocatalyst, the lifetime of the catalyst was investigated, because it gives an impact on cost-effectiveness. Radical trapping experiments were conducted to assess the contribution of •OH radicals, h + , O2, and (•O2-

) generated during solar light irradiation. The mineralization of the compounds AMX, OFLX, CTZ, and DOX were confirmed in terms of reduction TOC. Experimentally it was determined that synthesized photocatalyst could degrade model pollutant

compounds excellently due to its large surface area and high separation efficiency of photo- generated carriers with high oxidation and reduction capabilities. The photocatalytic reusability

was investigated for up to several successive cycles, and the composite particles maintained their high photodegradation activity for DOX and OFLX. Out of the various prepared catalysts, TSFC1 performed best without the oxidants, depicted good stability, and did not lose significant activity after re-use till seven cycles. The total cost, reaction rate, and recyclability studies confirmed that TSFC1 is a promising catalyst for photocatalytic degradation of selected compounds. Moreover, the appropriate dopant amount in TiO2-SiO2 was conducive to enhancing the sunlight photocatalytic activity proposing a promising environmentally compatible technology.