The degradation of paraben preservatives: Recent progress and sustainable approaches toward photocatalysis

Highlights

• Parabens, emerging contaminants, have been found in various environmental matrices.

• Photocatalysis is a promising, sustainable alternative to eliminate paraben preservatives.

• Different side-chain structures have a difference in mechanism and catalytic efficiency.

• Several types include ZnO-, ABO₃- perovskite, Ag-, Bi-, WO₃-based photocatalysts, are proposed.

• Many types of reactive species, such as.^●OH, ^●O₂⁻, ^●OOH, etc., are responsible for photocatalysis

Abstract

Parabens are a class of compounds primarily used as antimicrobial preservatives in pharmaceutical products, cosmetics, and foodstuff. Their widely used field leads to increasing concentrations detected in various environmental matrices like water, soil, and sludges, even detected in human tissue, blood, and milk. Treatment techniques, including chemical advanced oxidation, biological degradation, and physical adsorption processes, have been widely used to complete mineralization or to degrade parabens into less complicated byproducts. All kinds of processes were reviewed to give a completed picture of parabens removal. In light of these treatment techniques, advanced photocatalysis, which is emerging rapidly and widely as an economical, efficient, and environmentally-friendly technique, has received considerable attention. TiO₂-based and non-TiO₂-based photocatalysts play an essential role in parabens degradation. The effect of experimental parameters, such as the concentration of targeted parabens, concentration of photocatalyst, reaction time, and initial solution pH, even the presence of radical scavengers, are surveyed and compared from the literature. Some representative parabens such as methylparaben, propylparaben, and benzylparaben have been successfully studied the reaction pathways and their intermediates in their degradation process. As reported in the literature, the degradation of parabens involves the production of highly reactive species, mainly hydroxyl radicals. These reactive radicals would attack the paraben preservatives, break, and finally mineralize them into simpler inorganic and nontoxic molecules. Concluding perspectives on the challenges and opportunities for photocatalysis toward parabens remediation are also intensively highlighted.

Introduction

To date, water is an essential commodity for the existence of life on earth. However, pollution of water makes life difficult. In recent days, water pollution is predominantly due to the inappropriate or inadequate treatment of the wastewater and the substantial disposal into the water bodies (Gerlak et al., 2018). A plethora of pollutants exist in their chemical forms, thus contaminating the water bodies. Among them, pharmaceuticals and personal care products (PPCPs) are widespread, persistent pollutants from anthropogenic sources (Soon and Hameed, 2011; Kanakaraju et al., 2018). Parabens are a class of compounds primarily used as antimicrobial preservatives in pharmaceutical products in the mid-1920s (Elder, 1984). However, the use of parabens has extended as preservatives, antimicrobial agents, antifungal agents in cosmetics, and foodstuff (Matwiejczuk et al., 2020). The antimicrobial activity is due to the multiple biological actions, including inhibitory effects on membrane transport. Parabens have been detected in increasing concentrations in various environmental matrices like water, soil, and sludge in concentrations ranging from several ng·L⁻¹ to μg·L⁻¹. They have been found in human tissue, blood, and milk, indicating the transport of parabens from the environment to human beings, thereby affecting human health (Golden et al., 2005; Grecco et al., 2018). Due to the potential threat to human beings and wild-life, these parabens have been included in the list of emerging environmental pollutants by the U.S. Environmental Protection Agency.

Due to the increasing concern about water pollution, there is an urgent need to develop effective treatments to eliminate environmental waters. Some of the common processes used for water pollution treatment, including sono-electrocoagulation (Moradi et al., 2021), vacuum membrane distillation (Dragoi and Vasseghian, 2020), photocatalysis (Li et al., 2018; Bhuvaneswari et al., 2020; Dutta et al., 2020; Huang et al., 2020b; Lam et al., 2020; Nguyen et al., 2020a, 2020d, 2021; Palanisamy et al., 2020; Raizada et al., 2020; Sharma et al., 2020a, 2020b; Sudhaik et al., 2020a, 2020b; Thakur et al., 2020; Vu et al., 2020; Kumar et al., 2021; Patial et al., 2021; Smaali et al., 2021), adsorption (Dan et al., 2021; Raizada et al., 2021), bioadsorption (Wu and Yu, 2006), phytoremediation (Wei et al., 2021), ozonation (Rout et al., 2021), advanced electrochemical oxidation (Divyapriya et al., 2021), etc., have also been discussed. In light of the potential abatement techniques for paraben preservatives, several treatment processes, such as adsorption (Liu et al., 2009), and biological oxidation (Liu et al., 2009) have been successfully proposed. However, it notes that adsorption processes are only employed for phase separation of parabens from the matrix. Several of these methods could not achieve higher degradation efficiency, particularly in ambient, experimental conditions, or demands substantial energy inputs. In light of these treatment techniques, advanced oxidation processes (AOPs), including photocatalysis (Frontistis et al., 2017b; Kotzamanidi et al., 2018), photolysis (Gomes et al., 2018), electrochemical oxidation (Steter et al., 2014b; Domínguez et al., 2016; Frontistis et al., 2017c; Moradi et al., 2020b; Pueyo et al., 2020), sonochemical degradation (Sasi et al., 2015; Savun-Hekimoğlu and Ince, 2019), Fenton reagent (Martins et al., 2016), photo-Fenton (Lucas and Peres, 2015), sono-photo-Fenton (Moradi et al., 2020a), ozone oxidation (Asgari et al., 2019), photodegradation (Gmurek et al., 2015; Velegraki et al., 2015; Álvarez et al., 2020; Petala et al., 2020), UV/H₂O₂ (BŁędzka et al., 2010), have attracted great attention of researchers. Since AOPs include oxidation/reduction reactions involving various highly reactive radical species, these processes could not selectively degrade the contaminant candidates into final mineralization products. Though there are many review articles on the treatment of PPCPs, a particular spotlight on parabens is of interest (Sui et al., 2015; Wang and Wang, 2016; Yang et al., 2017; Awfa et al., 2018). To the best of our knowledge, this is the first review available dedicated to photocatalytic degradation of parabens, including TiO₂ and non-TiO₂ based photocatalytic catalysts and both UV and solar irradiation.

The present article critically reviews the available literature, mainly focusing on parabens as contaminant candidates and photocatalysis, as shown in Fig. 1. A comprehensive literature review on its properties, use, and technological processes is discussed before discussing photocatalytic degradation. Photocatalytic degradation of parabens has been critically reviewed and discussed in recent literature.