Binder-Free Immobilization of Photocatalyst on Membrane Surface for Efficient Photocatalytic H2O2 Production and Water Decontamination

Abstract

In photocatalytic water treatment processes, the particulate photocatalysts are typically immobilized on membrane, through either chemical/physical loading onto the surface or directly embedding in the membrane matrix. However, these immobilization strategies inevitably compromise the interfacial mass diffusion and cause activity decline relative to the suspended catalyst. Here, we propose a binder-free surface immobilization strategy for fabrication of high-activity photocatalytic membrane. Through a simple dimethylformamide (DMF) treatment, the nanofibers of polyvinylidene fluoride membrane were softened and stretched, creating enlarged micropores to efficiently capture the photocatalyst. Subsequently, the nanofibers underwent shrinking during DMF evaporation, thus firmly strapping the photocatalyst microparticles on the membrane surface. This surface self-bounded photocatalytic membrane, with firmly bounded yet highly exposed photocatalyst, exhibited 4.2-fold higher efficiency in hydrogen peroxide (H2O2) photosynthesis than the matrix-embedded control, due to improved O2 accessibility and H2O2 diffusion. It even outperformed the suspension photocatalytic system attributed to alleviated H2O2 decomposition at the hydrophobic surface. When adopted for UV-based water treatment, the photocatalytic system exhibited tenfold faster micropollutants photodegradation than the catalyst-free control and demonstrated superior robustness for treating contaminated tap water, lake water and secondary wastewater effluent. This immobilization strategy can also be extended to the fabrication of other photocatalytic membranes with diverse catalyst types and membrane substrate. Overall, our work opens a facile avenue for fabrication of high-performance photocatalytic membranes, which may benefit advanced oxidation water purification application and beyond.

1. Introduction

Water pollution by micropollutants, including various endocrine disrupting substances and antibiotics, has raised widespread ecological and health concerns [1–3]. However, low-carbon and economically affordable technologies for efficiently eliminating these micropollutants are still lacking [4]. In this respect, the UV/H2O2 advanced oxidation processes hold a great potential, due to less formation of toxic byproduct than the conventional UV/Cl2 processes for water disinfection and decontamination [5, 6]. In the UV/H2O2 process, the H2O2 oxidant undergoes photolysis to generate hydroxyl radicals (·OH) for pollutant degradation [7, 8]. Therefore, a continuous supply of H2O2, either through exogenous addition or through in situ generation, is needed to sustain the reaction [8–10].

Of particular interest is the in situ H2O2 generation by electrochemical or photocatalytic processes, which can avoid the complicated processes of H2O2 transportation and storage [11–13]. The technologies for H2O2 electrosynthesis have been well established to date, but their application niches have been mainly limited to saline wastewater and seawater which feature low ions migration resistance [14–17]. In comparison, H2O2 photosynthesis is adaptable to broader range of water matrix due to less restriction by solution conductivity [18–20] and allows for direct integration into UV water treatment process. Nevertheless, the limited activity of the photocatalytic systems presents a significant barrier to their practical environmental application. Especially, the immobilization of particulate photocatalyst onto a membrane substrate, which is typically essential for continuous-flow water treatment, always lead to activity decline [21–24]. In these systems, the catalyst was usually cross-linked to the membrane surface by using binders.