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Besides, the slow charge transfer kinetics of TiO 2 during photocatalysis leads to a negligible hydrogen evolution ability. [3] To tackle these problems, several approaches can be adopted, including the defect engineering, [4] dopants, [5] morphology design, [6] cocatalyst depositions, [7] and heterojunctions. [8] Recently, Step-scheme (S-scheme) heterojunction has emerged as an efficient structure to separate the charge carriers due to internal built electric field and maintained redox potential of electrons and holes. [9] The difference between the Fermi levels of the semiconductors allows electrons to transfer at the interface until the equilibrium of Fermi levels is reached. [10] S-scheme heterojunction is composed of an oxidative photocatalyst (OP) and a reductive photocatalyst (RP), thus the electron generated at the OP and the holes generated at the RP will be recombined at the interface. The electrons at the RP and holes at the OP can be efficiently separated through a step-type path. For example, Yu et al. have reported an S-scheme junction as TiO 2 /CdS for hydrogen evolution from water. [11] Khaled et al. recently investigate a tandem structure between TiO 2 , Bi 2 S 3, and MoS 2 , where the electron transfer can be tuned by the energy of the incident light. Under UV-vis illumination, electrons transfer from TiO 2 to MoS 2 and Bi 2 S 3 , showing an S-scheme heterojunction, however, under vis-NIR illumination, electrons transfer from Bi 2 S 3 and MoS 2 to TiO 2 , forming a type-II heterojunction. [12] In addition, two-dimensional (2D) materials have shown great potential in photocatalysis due to the laminar structure and high surface area, that allow free electron transport within and across the surface plane. [13] For example, the preparation of TiO 2 /g-C 3 N 4 S-Scheme junction improves the hydrogen evolution efficiency by a factor of 7.5 and 27.2, compared to bare g-C 3 N 4 and TiO 2 . [14] Except for carbonaceous materials, e.g., graphene and C 3 N 4 , [15] other 2D semiconductors, for example, transition metal dichalcogenides (TMDs), [16] transition metal oxides (TMOs), layered titanate, [2] 0D-2D composite [17] and 2D-2D composite [15b,17b] have attracted attention in the applications as electrochromics, [18] energy storage and photocatalysis. [19] Few-layered MoO 3 show high mobility in charge transport. [20] Furthermore, it shows broadened bandgap andThe intimate contact of components in a heterojunction photocatalyst is essential in determining the photocatalytic performance. To build a face-toface interface in a 2D-2D heterojunction is an effective strategy to improve the charge carrier separation and utilization efficiency. In this work, the fabrication of a Step-scheme heterojunction on thin titania (TiO 2 ) nanosheets with few-layered MoO 3 structures is reported. With a decoration of a low dose of MoO 3 layer by ball milling method, TiO 2 (B) shows a three-fold increase in the hydrogen evolution rate. The reaction mechanism and driving force of charge transfer in the S-scheme heteroj...

Photoreforming (PR) technology is a green and sustainable approach to tackling the environmental pollution problems generated by plastic waste. In this review, recent advances in the PR of plastic waste are summarized that include the design of photocatalysts, regulations on the products, and innovations on the PR devices and compared to traditional methods. The scientific principles of PR reactions in thermodynamics and kinetics are discussed, and approaches to improve the efficiency of PR reactions are proposed, that involve enhancement in light absorption ability, charge carrier migration/separation efficiency, and surface reaction rate. Particularly, the enhancement for H2 production in the PR reaction is highlighted, and the applications using large-scale reactors are discussed, with advantages and disadvantages of recent reactor configurations. In conclusion, the perspectives on the applications of PR in plastic degradation and hydrogen evolution are given. This review thus comprehensively summarizes scientific principles, challenges, and perspectives of PR reactions on plastic waste to improve the overall efficiency and potential to be applied in the industry.