A 3D C@TiO2 multishell nanoframe for simultaneous photothermal catalytic hydrogen generation and organic pollutant degradation

Synergistic hydrogen production and organic pollutant removal via dual-functional photocatalytic systems

Photocatalytic water splitting is a promising way to produce H2, a green and clean energy source. However, efficient H2 production typically relies on the addition of electron donors, such as alcohols and acids, which are neither environmentally friendly nor cost-effective. Recently, we have witnessed a surge of studies in coupling photocatalytic H2 evolution with organic pollutant oxidation, which significantly promotes charge separation and improves the overall photocatalytic efficiency. It is thus an opportune time to critically assess the recent literature concerning dual-functional photocatalytic systems and provide perspectives for its future development. In this minireview, we begin with the working principles and requirements for synergistic photocatalytic systems. We then summarize and critically discuss the recent advances in photocatalytic H2 production and the degradation of various organic pollutants, including antibiotics, dyes, and phenols. Finally, we discuss the current challenges and suggest future directions for this field.

MIL-125-PDI/ZnIn2S4 Inorganic-Organic S-Scheme Heterojunction With Hierarchical Hollow Nanodisc Structure for Efficient Hydrogen Evolution from Antibiotic Wastewater Remediation

Efficient photocatalytic production of H2 from wastewater is expected to address environmental pollution and energy crises effectively. However, the rapid recombination of photoinduced carriers results in low photoconversion efficiency. At present, inorganic-organic S-scheme heterojunction have become a prominent and promising technology. In this study, an organic ligand modified MIL-125-PDI/ZnIn2S4 (ZIS) inorganic-organic S-scheme heterojunction catalyst is designed. ZIS nanosheets are grown on the disc-shaped MIL-125-PDI surface to form a distinctive hollow nanodiscs with hierarchical structure, giving the material an abundance of surface active sites, an optimized electronic structure, and a spatially separated redox surface. Consequently, the optimal 100MIL-125-PDI250/ZIS exhibited high photocatalytic HER of 508.99 µmol g-1 h-1 in Tetracycline hydrochloride (TC-HCl) solution. Meanwhile, the catalyst achieved complete TC-HCl removal and mineralization rate of 66.62% in 4 h. Experimental and theoretical calculations corroborate that the staggered band alignment and work function difference between MIL-125-PDI and ZIS induce the formation of a built-in electric field, thus regulating the charge transfer routes and consequently enhancing charge separation efficiency. The possible photocatalytic mechanism is analyzed using liquid chromatography-mass spectrometry (LC-MS), and the toxicities of the degradation products are also evaluated. This work presents a green dual-function strategy for H2 production and antibiotic wastewater recycling.

Selective efficient photocatalytic degradation of antibiotics and direct Z-type migration pathway for hierarchical core-shell TiO2/g-C3N4 composites

Constructing superior Z-type photocatalytic heterojunction is beneficial to effectively enlarge interface contact, improve the photo-generated carrier separation rate, and retain the high redox ability. In this work, we designed a hierarchical core-shell g-C3N4/TiO2 structure to build Z-type heterojunction via combining simple template method and pyrolysis process. A close-knit Z-type heterojunction was constructed using TiO2 as a thick core and g-C3N4 as an ultra-thin shell. The effects of lamp source, wavelength, tetracycline (TC) concentration, and photocatalyst dose on the degradation performance on TC of g-C3N4/TiO2 were inspected. 0.1TiO2/g-C3N4 photocatalyst had the best degradation rate and highest removal rate within 30 min, and its degradation rate was about 49, 23, and 5 times than pure g-C3N4, TiO2, and commercial TiO2/g-C3N4 in respect. Moreover, compared with degradation ability under Xenon lamp, LED irradiation for g-C3N4/TiO2 composites showed a remarkable selective degradation. The fast and efficient Z-type transfer pathway of 0.1 g-C3N4/TiO2 was realized by forming an optimized interface and abundant surface active sites ascribed to the combined action of thick TiO2 core and ultra-thin g-C3N4 shell. In addition, the degradation intermediates were analyzed by LC-MS and suggested pathways of degradation. The work could provide novel design concept to obtain reliable Z-type photocatalysts with hierarchical core-shell structure applied in degradation of antibiotic wastewater.

Hybrid Aeromaterials for Enhanced and Rapid Volumetric Photothermal Response

Conversion of light into heat is essential for a broad range of technologies such as solar thermal heating, catalysis and desalination. Three-dimensional (3D) carbon nanomaterial-based aerogels have been shown to hold great promise as photothermal transducer materials. However, until now, their light-to-heat conversion is limited by near-surface absorption, resulting in a strong heat localization only at the illuminated surface region, while most of the aerogel volume remains unused. We present a fabrication concept for highly porous (>99.9%) photothermal hybrid aeromaterials, which enable an ultrarapid and volumetric photothermal response with an enhancement by a factor of around 2.5 compared to the pristine variant. The hybrid aeromaterial is based on strongly light-scattering framework structures composed of interconnected hollow silicon dioxide (SiO2) microtubes, which are functionalized with extremely low amounts (in order of a few μg cm-3) of reduced graphene oxide (rGO) nanosheets, acting as photothermal agents. Tailoring the density of rGO within the framework structure enables us to control both light scattering and light absorption and thus the volumetric photothermal response. We further show that by rapid and repeatable gas activation, these transducer materials expand the field of photothermal applications, like untethered light-powered and light-controlled microfluidic pumps and soft pneumatic actuators.

Recent Advances in Graphitic Carbon Nitride Based Electro-Catalysts for CO2 Reduction Reactions

The electrocatalytic carbon dioxide reduction reaction is an effective means of combating the greenhouse effect caused by massive carbon dioxide emissions. Carbon nitride in the graphitic phase (g-C₃N₄) has excellent chemical stability and unique structural properties that allow it to be widely used in energy and materials fields. However, due to its relatively low electrical conductivity, to date, little effort has been made to summarize the application of g-C₃N₄ in the electrocatalytic reduction of CO₂. This review focuses on the synthesis and functionalization of g-C₃N₄ and the recent advances of its application as a catalyst and a catalyst support in the electrocatalytic reduction of CO₂. The modification of g-C₃N₄-based catalysts for enhanced CO₂ reduction is critically reviewed. In addition, opportunities for future research on g-C₃N₄-based catalysts for electrocatalytic CO₂ reduction are discussed.

Thermally-enhanced sono-photo-catalysis by defect and facet modulation of Pt-TiO2 catalyst for high-efficient hydrogen evolution

Sono-photo-catalysis (SPC) has been regarded as a promising route for hydrogen evolution from water splitting due to the sono-photo-synergism, whereas its current performance (∼μmol g-1 h-1) is yet far from expectation. Herein, we give the first demonstration that the intrinsically coupled thermal effects of light and ultrasound, which is normally underestimated or neglected, can simultaneously reshape the photo- and sono-catalytic activities for hydrogen evolution and establish a higher degree of synergy between light and ultrasound in SPC even on the traditional Pt-TiO2 catalyst. A high-efficient hydrogen evolution rate of 225.04 mmol g-1 h-1 with light-to‑hydrogen efficiency of 0.89% has been achieved in thermally-enhanced SPC, which is an order of magnitude higher than that without thermal effects. More impressively, the increase of synergy index up to 53% has been achieved. Through experiments and theoretical calculations, the thermally-enhanced sono-photo-synergism is attributed to the sono-photo-thermo-modulated structural optimization of defect-rich TiO2 support and deaggregated Pt species with functional complementary lattice facets, which optimizes not only the thermodynamic properties by enhancing light harvesting and the charge redox power, but also the kinetic properties by accelerating the net efficiency of charge separation and the whole processes of water splitting, including the dissociation of water molecules on high-index (200) Pt facets and production of H∗ intermediates on defect-rich TiO2-x support and low-index (111) Pt facets. This study exemplifies that coupling light- and ultrasonic-induced thermal effects in SPC system could enhance the synergy between light and ultrasound by modulating catalyst structure to achieve double optimization of thermodynamic and kinetic properties of SPC hydrogen evolution.

Recent Advancements in Photocatalysis Coupling by External Physical Fields

Photocatalysis is one of the most promising green technologies to utilize solar energy for clean energy achievement and environmental governance, such as artificial photosynthesis, water splitting, pollutants degradation, etc. Despite decades of research, the performance of photocatalysis still falls far short of the requirement of 5% solar energy conversion efficiency. Combining photocatalysis with the other physical fields has been proven to be an efficient way around this barrier which can improve the performance of photocatalysis remarkably. This review will focus on the recent advances in photocatalysis coupling by external physical fields, including Thermal-coupled photocatalysis (TCP), Mechanical-coupled photocatalysis (MCP), and Electromagnetism-coupled photocatalysis (ECP). In this paper, coupling mechanisms, materials, and applications of external physical fields are reviewed. Specifically, the promotive effect on photocatalytic activity by the external fields is highlighted. This review will provide a detailed and specific reference for photocatalysis coupling by external physical fields in a deep-going way.

Hollow Nanoboxes Cu2-x S@ZnIn2 S4 Core-Shell S-Scheme Heterojunction with Broad-Spectrum Response and Enhanced Photothermal-Photocatalytic Performance

Major issues in photocatalysis include improving charge carrier separation efficiency at the interface of semiconductor photocatalysts and rationally developing efficient hierarchical heterostructures. Surface continuous growth deposition is used to make hollow Cu_2-x S nanoboxes, and then simple hydrothermal reaction is used to make core-shell Cu_2-x S@ZnIn₂ S₄ S-scheme heterojunctions. The photothermal and photocatalytic performance of Cu_2-x S@ZnIn₂ S₄ is improved. In an experimental hydrogen production test, the Cu_2-x S@ZnIn₂ S₄ photocatalyst produces 4653.43 µmol h^-1 g^-1 of hydrogen, which is 137.6 and 13.8 times higher than pure Cu_2-x S and ZnIn₂ S₄ , respectively. Furthermore, the photocatalyst exhibits a high tetracycline degradation efficiency in the water of up to 98.8%. For photocatalytic reactions, the hollow core-shell configuration gives a large specific surface area and more reactive sites. The photocatalytic response range is broadened, infrared light absorption enhanced, the photothermal effect is outstanding, and the photocatalytic process is promoted. Meanwhile, characterizations, degradation studies, active species trapping investigations, energy band structure analysis, and theoretical calculations all reveal that the S-scheme heterojunction can efficiently increase photogenerated carrier separation. This research opens up new possibilities for future S-scheme heterojunction catalyst design and development.