Photocatalytic Evolution of Hydrogen Peroxide: A Minireview

Abstract

Hydrogen peroxide (H2O2) has demonstrated applicability in a wide range of applications, spanning from a bleaching agent in the pulp industry, environmental remediation, and fuel cell technology. Industrial scale synthesis, either by the anthraquinone method or catalytic oxidation of hydrogen gas, has serious drawbacks which are related with energy demanding and multi-step processes. An alternative green strategy involves the photocatalytic synthesis of H2O2. All that is needed is the renewable energy of the sun, a semiconducting species absorbing in the visible region, water, and oxygen. In this minireview, we describe the evolution of research milestones that have been achieved within the recent decades regarding the development of functional photocatalytic systems. In the early studies, back in the 1980’s, TiO2-based systems were mostly investigated. However, due to the large band gap of titania (3.2 eV), alternative semiconductors were studied which strongly absorb in the visible region. Thus, a variety of semiconductor families have been investigated, such as doped titania systems, other metal oxides, metal sulfides, organic semiconductors, metal-organic frameworks, carbon nitride systems, etc. In parallel, the development of functional dopants onto the surface of the main semiconductor has lead to both the inhibition of electron-hole recombination and H2O2 degradation. The current minireview collectively provides the studies of the higher H2O2 production rates and offer some suggestions for the near future.

Boosting Carbon Nitride Photoactivity by Metal-Free Functionalization for Selective H2O2 Synthesis under Visible Light

“…By adding increasing amounts of IPA in the aqueous solution (Figure S9), it is possible to observe an increase in the production of H 2 O 2 until 90% IPA/water, ascribed to a higher availability of protons , and an increased solubility of oxygen . The partial oxidation of IPA releases protons that will aid the photocatalytic process, by offering the required hydrogen component for H 2 O 2 production, besides reducing the recombination process through an increase of hole-oxidation. , An optimal amount of 90% IPA/water was observed, as a higher concentration of IPA leads to a reduction in the H 2 O 2 yield probably due to the scavenging effect that IPA demonstrates toward holes and reactive oxygen species . Also, the presence of both water and alcohol allows for the generation of various reactive species and potentiates the necessary redox reactions …”

“…102,110 An optimal amount of 90% IPA/water was observed, as a higher concentration of IPA leads to a reduction in the H 2 O 2 yield probably due to the scavenging effect that IPA demonstrates toward holes and reactive oxygen species. 112 Also, the presence of both water and alcohol allows for the generation of various reactive species and potentiates the necessary redox reactions. 113 In the presence of IPA (Figure 9a), which is a very strong proton donor, the reaction shown in eq 2 was accelerated, leading to a higher H 2 O 2 generation (eq 3).…”

Hydrogen Peroxide Production by Inorganic Photocatalysts Consisting of Gold Nanoparticle and Metal Oxide toward Oxygen Cycle Chemistry

“…A promising route is the photocatalytic production of H 2 O 2 via two electron-oxygen reduction reaction (2e – -ORR). Seminal mechanistic studies on TiO 2 -photocatalyzed reactions in the presence of O 2 showed that a few μM levels of H 2 O 2 is generated by ORR. − Since the report on the gold-nanoparticle-loaded TiO 2 (Au/TiO 2 )-photocatalyzed synthesis of H 2 O 2 more than 10 mM via 2e – -ORR by ethanol in 2010 (eq ), the research on the photocatalytic H 2 O 2 synthesis has been widely and intensively pursued. , The combination of the reaction in eq with the natural photosynthesis can form a carbon neutral cycle for H 2 O 2 production because ethanol is a typical biomass-derived compound.where Δ r G 0 is the standard Gibbs energy of reaction.…”

“…8−11 Since the report on the gold-nanoparticle-loaded TiO 2 (Au/ TiO 2 )-photocatalyzed synthesis of H 2 O 2 more than 10 mM via 2e − -ORR by ethanol in 2010 (eq 1), 12 the research on the photocatalytic H 2 O 2 synthesis has been widely and intensively pursued. 13,14 The combination of the reaction in eq 1 with the natural photosynthesis can form a carbon neutral cycle for H 2 O 2 production because ethanol is a typical biomass-derived compound.…”

A general interfacial-energetics-tuning strategy for enhanced artificial photosynthesis

“…Solar energy is deemed as a key solution to the increasing global demands on clean energy and related climate issues 1 – 3 . To tackle the spatiotemporal fluctuations of solar radiation, a promising strategy is to capture solar energy in storable and transportable solar fuels (e.g., H 2 and H 2 O 2 ) by artificial photosynthesis 4 , 5 . Among primary photosynthetic systems, the particulate photocatalyst is considered as the most cost-effective one because of its high simplicity and scalability, yet its energy conversion efficiency still needs improving for viable applications 6 , 7 .…”