Nanoarchitectonics of MXene/semiconductor heterojunctions toward artificial photosynthesis via photocatalytic CO2 reduction

CdS-based Schottky junctions for efficient visible light photocatalytic hydrogen evolution

Heterojunctions photocatalysts play a crucial role in achieving high solar-hydrogen conversion efficiency. In this work, we mainly focus on the charge transfer dynamics and pathways for sulfides-based Schottky junctions in the photocatalytic water splitting process to clarify the mechanism of heterostructures photocatalysis. Sulfides-based Schottky junctions (CdS/CoP and CdS/1T-MoS2) were successfully constructed for photocatalytic water splitting. Because of the higher work function of CdS than that of CoP and 1T-MoS2, the direction of the built-in electric field is from CoP or 1T-MoS2 to semiconductor. Therefore, CoP and 1T-MoS2 can act as electrons acceptors to accelerate the transfer of photo-generated electron on the surface of CdS, thus improving the charge utilization efficiency. Meanwhile, CoP and 1T-MoS2 as active sites can also promote the water dissociation and lower the H+ reduction overpotential, thus contributing to the excellent photocatalytic hydrogen production activity (23.59 mmol·h-1·g-1 and 1195.8 mol·h-1·g-1 for CdS/CoP and CdS/1T-MoS2).

Physicochemical Modulations in MXenes for Carbon Dioxide Mitigation and Hydrogen Generation: Tandem Dialogue between Theoretical Anticipations and Experimental Evidences

The dawn of MXenes has fascinated researchers under their intriguing physicochemical attributes that govern their energy and environmental applications. Modifications in the physicochemical properties of MXenes pave the way for efficient energy-driven operations such as carbon capture and hydrogen generation. The physicochemical modulations such as interface engineering through van der Waals coupling with homo/hetero-junctions render the tunability of optoelectronic variables driving the photochemical and electrochemical processes. Herein, we have reviewed the recent achievements in physicochemical properties of MXenes by highlighting the role of intercalants/terminal groups, atomic defects, surface chemistry and few/mono-layer formation. Recent findings of MXenes-based materials are systematically surveyed in a tandem manner with the future outlook for constructing next-generation multi-functional catalytic systems. Theoretical modelling of MXenes surface engineering proffers the mechanistic comprehension of surface phenomena such as termination, interface formation, doping and functionalization, thereby enabling the researchers to exploit them for targeted applications. Therefore, theoretical anticipations and experimental evidences of electrochemical/photochemical carbon dioxide reduction and hydrogen evolution reactions are synergistically discussed.

Recent advances of metal active sites in photocatalytic CO2 reduction

Photocatalytic CO2 reduction captures solar energy to convert CO2 into hydrocarbon fuels, thus shifting the dependence on rapidly depleting fossil fuels. Among the various proposed photocatalysts, systems containing metal active sites (MASs) possess obvious advantages, such as effective photogenerated carrier separation, suitable adsorption and activation of intermediates, and achievable C-C coupling to generate multi-carbon (C2+) products. The present review aims to summarize the typical photocatalytic materials with MAS, highlighting the critical role of different formulations of MAS in CO2 photoreduction, especially for C2+ product generation. State-of-the-art progress in the characterization and theoretical calculations for MAS-containing photocatalysts is also emphasized. Finally, the challenges and prospects of catalytic systems involving MAS for solar-driven CO2 conversion are outlined, providing inspiration for the future design of materials for efficient photocatalytic energy conversion.

Enhanced conversion of CO2 into C2H4 on single atom Cu-anchored graphitic carbon nitride: Synergistic diatomic active sites interaction

Single atom metal-nitrogen-carbon materials have emerged as remarkably potent catalysts, demonstrating unprecedented potential for the photo-driven reduction of CO2. Herein, a unique Cu@g-C3N5 catalyst obtained by cooperation of single atom Cu and nitrogen-rich g-C3N5 is proposed. The particular CuN diatomic active sites (DAS) in Cu@g-C3N5 contribute to the formation of highly stable CuOCN adsorption, a key configuration for CO2 activation and CC coupling. The synergistic diatomic active sites interaction is found responsible for the efficient photoreduction of CO2 to C2H4 which has been demonstrated in our Gibbs free energy calculation and COHP analysis. The CO2 activation mechanism was studied, the charge density difference and DOS analysis show that the low oxidation state Cu atom significantly affects the electronic structure of g-C3N5 and then enhance the catalytic activity of CO2 hydrogenation.

Titanium carbide sealed cadmium sulfide quantum dots on carbon, oxygen-doped boron nitride for enhanced and durable photochemical carbon dioxide reduction

Despite great efforts that have been made, photocatalytic carbon dioxide (CO2) reduction still faces enormous challenges due to the sluggish kinetics or disadvantageous thermodynamics. Herein, cadmium sulfide quantum dots (CdS QDs) were loaded onto carbon, oxygen-doped boron nitride (BN) and encapsulated by titanium carbide (Ti3C2, MXene) layers to construct a ternary composite. The uniform distribution of CdS QDs and the tight interfacial interaction among the three components could be achieved by adjusting the loading amounts of CdS QDs and MXene. The ternary 100MX/CQ/BN sample gave a productive rate of 2.45 and 0.44 μmol g-1 h-1 for carbon monoxide (CO) and methane (CH4), respectively. This CO yield is 1.93 and 6.13 times higher than that of CdS QDs/BN and BN counterparts. The photocatalytic durability of the ternary composite is significantly improved compared with CdS QDs/BN because MXene can protect CdS from photocorrosion. The characterization results demonstrate that the excellent CO2 adsorption and activation capabilities of BN, the visible light absorption of CdS QDs, the good conductivity of MXene and the well-matched energy band alignment jointly promote the photocatalytic performance of the ternary catalyst.

The Synthesis, Structural Characterization, and DFT Calculation of a New Binuclear Gd(III) Complex with 4-Aacetylphenoxyacetic Acid and 1,10-Phenanthroline Ligands and Its Roles in Catalytic Activity

A new binuclear Gd(III) complex, [Gd2(L)6(Phen)2]·4H2O, was synthesized via the reaction of gadolinium(III) nitrate hexahydrate, 4-acetylphenoxyacetic acid (HL), NaOH, and 1,10-phenanthroline (Phen) in a solution of water-ethanol (v:v = 1:1). The Gd(III) complex was characterized using IR, UV-vis, TG-DSC, fluorescence, and single-crystal X-ray diffraction analyses. The results showed that the Gd(III) complex crystallizes in the triclinic system, space group P-1, and each Gd(III) ion was coordinated with two nitrogen atoms (N1, N2, or N1a, and N2a) from two Phen ligands and seven oxygen atoms (O1, O2, O7a, O9, O8, O8a, O10a, or O1a, O2a, O7, O8, O8a, O9a, and O10) from six L ligands, respectively, forming a nine-coordinated coordination mode. The Gd(III) complex molecules formed a one-dimensional chained and three-dimensional network structure via benzenering π-π stacking. The Hirschfeld surface analysis and the calculations of the electron density distributions of the frontier molecular orbitals of the Gd(III) complex were performed. The catalytic activities of the photocatalytic CO2 reduction and benzyl alcohol oxidation using the Gd(III) complex as a catalyst were performed. The results of the photocatalytic CO2 reduction showed that the yield and the selectivity of CO reached 41.5 μmol/g and more than 99% after four hours, respectively. The results of the benzyl alcohol oxidation showed that the yield of benzaldehyde was 45.7% at 120 °C with THF as the solvent under 0.5 MPa O2 within 2 h.

Cobalt-based Polymerized Porphyrinic Network for Visible-light-driven CO2 Reduction

Visible-light-driven conversion of carbon dioxide to valuable compounds and fuels is an important but challenging task due to the inherent stability of the CO2 molecules. Herein, we report a series of cobalt-based polymerized porphyrinic network (PPN) photocatalysts for CO2 reduction with high activity. The introduction of organic groups results in the addition of more conjugated electrons to the networks, thereby altering the molecular orbital levels within the networks. This integration of functional groups effectively adjusts the levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). The PPN(Co)-NO2 exhibits outstanding performance, with a CO evolution rate of 12 268 μmol/g/h and 85.8% selectivity, surpassing most similar photocatalyst systems. The performance of PPN(Co)-NO2 is also excellent in terms of apparent quantum yield (AQY) for CO production (5.7% at 420 nm). Density functional theory (DFT) calculations, time-resolved photoluminescence (TRPL), and electrochemical tests reveal that the introduction of methyl and nitro groups leads to a narrower energy gap, facilitating a faster charge transfer. The coupling reaction in this study enables the formation of stable C-C bonds, enhancing the structural regulation, active site diversity, and stability of the catalysts for photocatalytic CO2 reduction. This work offers a facile strategy to develop reliable catalysts for efficient CO2 conversion.

Review on Microreactors for Photo-Electrocatalysis Artificial Photosynthesis Regeneration of Coenzymes

In recent years, with the outbreak of the global energy crisis, renewable solar energy has become a focal point of research. However, the utilization efficiency of natural photosynthesis (NPS) is only about 1%. Inspired by NPS, artificial photosynthesis (APS) was developed and utilized in applications such as the regeneration of coenzymes. APS for coenzyme regeneration can overcome the problem of high energy consumption in comparison to electrocatalytic methods. Microreactors represent a promising technology. Compared with the conventional system, it has the advantages of a large specific surface area, the fast diffusion of small molecules, and high efficiency. Introducing microreactors can lead to more efficient, economical, and environmentally friendly coenzyme regeneration in artificial photosynthesis. This review begins with a brief introduction of APS and microreactors, and then summarizes research on traditional electrocatalytic coenzyme regeneration, as well as photocatalytic and photo-electrocatalysis coenzyme regeneration by APS, all based on microreactors, and compares them with the corresponding conventional system. Finally, it looks forward to the promising prospects of this technology.

Molecular machines working at interfaces: physics, chemistry, evolution and nanoarchitectonics

As a post-nanotechnology concept, nanoarchitectonics combines nanotechnology with advanced materials science. Molecular machines made by assembling molecular units and their organizational bodies are also products of nanoarchitectonics. They can be regarded as the smallest functional materials. Originally, studies on molecular machines analyzed the average properties of objects dispersed in solution by spectroscopic methods. Researchers' playgrounds partially shifted to solid interfaces, because high-resolution observation of molecular machines is usually done on solid interfaces under high vacuum and cryogenic conditions. Additionally, to ensure the practical applicability of molecular machines, operation under ambient conditions is necessary. The latter conditions are met in dynamic interfacial environments such as the surface of water at room temperature. According to these backgrounds, this review summarizes the trends of molecular machines that continue to evolve under the concept of nanoarchitectonics in interfacial environments. Some recent examples of molecular machines in solution are briefly introduced first, which is followed by an overview of studies of molecular machines and similar supramolecular structures in various interfacial environments. The interfacial environments are classified into (i) solid interfaces, (ii) liquid interfaces, and (iii) various material and biological interfaces. Molecular machines are expanding their activities from the static environment of a solid interface to the more dynamic environment of a liquid interface. Molecular machines change their field of activity while maintaining their basic functions and induce the accumulation of individual molecular machines into macroscopic physical properties molecular machines through macroscopic mechanical motions can be employed to control molecular machines. Moreover, research on molecular machines is not limited to solid and liquid interfaces; interfaces with living organisms are also crucial.

Preparation of highly dispersed Ni single-atom doped ultrathin g-C3N4 nanosheets by metal vapor exfoliation for efficient photocatalytic CO2 reduction

Single-atom photocatalysts can modulate the utilization of photons and facilitate the migration of photogenerated carriers. However, the preparation of single-atom uniformly doped photocatalysts is still a challenging topic. Herein, we propose the preparation of Ni single-atom doped g-C3N4 photocatalysts by metal vapor exfoliation. The Ni vapor produced by calcining nickel foam at high temperature accumulates in between g-C3N4 layers and poses a certain vapor pressure to destroy the interlayer van der Waals forces of g-C3N4. Individual metal atoms are doped into the structure while exfoliating g-C3N4 into nanosheets by metal vapor. Upon optimization of Ni content, the Ni single atom doped g-C3N4 nanosheets with 2.81 wt% Ni exhibits the highest CO2 reduction performance in the absence of sacrificial agents. The generation rates of CO and CH4 are 19.85 and 1.73 μmol g-1h-1, respectively. The improved photocatalytic performance is attributed to the anchoring Ni of single atoms on g-C3N4 nanosheets, which increases both carrier separation efficiency and reaction sites. This work provides insight into the design of photocatalysts with highly dispersed single-atom.

Antenna Effect in Noble Metal-Free Dye-Sensitized Photocatalytic Systems Enhances CO2 -to-CO Conversion

Dye-sensitized photocatalytic systems (DSPs) have been extensively investigated for solar-driven hydrogen (H2 ) evolution. However, their application in carbon dioxide (CO2 ) reduction remains limited. Furthermore, current solar-driven CO2 -to-CO DSPs typically employ rhenium complexes as catalysts. In this study, we have developed DSPs that incorporate noble metal-free components, specifically a zinc-porphyrin as photosensitizer (PS) and a cobalt-quaterpyridine as catalyst (CAT). Taking a significant stride forward, we have achieved an antenna effect for the first time in CO2 -to-CO DSPs by introducing a Bodipy as an additional chromophore to enhance light harvesting efficiency. The energy transfer from Bodipy to zinc porphyrin resulted in remarkable stability (turn over number (TON)=759 vs. CAT), and high CO evolution activity (42 mmol g-1  h-1 vs. CAT).

Synthesis, Structural Characterization, Hirschfeld Surface Analysis, Density Functional Theory, and Photocatalytic CO2 Reduction Activity of a New Ca(II) Complex with a Bis-Schiff Base Ligand

A new bis-Schiff base (L) Ca(II) complex, CaL, was synthesized by the reaction of calcium perchlorate tetrahydrate, 1,3-diamino-2-hydroxypropane, and 2-formyl phenoxyacetic acid in an ethanol-water (v:v = 2:1) solution and characterized by IR, UV-vis, TG-DTA, and X-ray single crystal diffraction analysis. The structural analysis indicates that the Ca(II) complex crystallizes in the monoclinic system, space group P121/n1, and the Ca(II) ions are six-coordinated with four O atoms (O8, O9, O11, O12, or O1, O2, O4, O6) and two N atoms (N1, N2, or N3, N4) of one bis-Schiff base ligand. The Ca(II) complex forms a tetramer by intermolecular O-H…O hydrogen bonds. The tetramer units further form a three-dimensional network structure by π-π stacking interactions of benzene rings. The Hirschfeld surface of the Ca(II) complex shows that the H…H contacts represent the largest contribution (41.6%) to the Hirschfeld surface, followed by O…H/H…O and C…H/H…C contacts with contributions of 35.1% and 18.1%, respectively. To understand the electronic structure of the Ca(II) complex, the DFT calculations were carried out. The photocatalytic CO2 reduction test of the Ca(II) complex exhibited a yield of 47.9 μmol/g (CO) and a CO selectivity of 99.3% after six hours.

2D Materials Nanoarchitectonics for 3D Structures/Functions

It has become clear that superior material functions are derived from precisely controlled nanostructures. This has been greatly accelerated by the development of nanotechnology. The next step is to assemble materials with knowledge of their nano-level structures. This task is assigned to the post-nanotechnology concept of nanoarchitectonics. However, nanoarchitectonics, which creates intricate three-dimensional functional structures, is not always easy. Two-dimensional nanoarchitectonics based on reactions and arrangements at the surface may be an easier target to tackle. A better methodology would be to define a two-dimensional structure and then develop it into a three-dimensional structure and function. According to these backgrounds, this review paper is organized as follows. The introduction is followed by a summary of the three issues; (i) 2D to 3D dynamic structure control: liquid crystal commanded by the surface, (ii) 2D to 3D rational construction: a metal-organic framework (MOF) and a covalent organic framework (COF); (iii) 2D to 3D functional amplification: cells regulated by the surface. In addition, this review summarizes the important aspects of the ultimate three-dimensional nanoarchitectonics as a perspective. The goal of this paper is to establish an integrated concept of functional material creation by reconsidering various reported cases from the viewpoint of nanoarchitectonics, where nanoarchitectonics can be regarded as a method for everything in materials science.

Visible Light Photoactivity of g-C3N4/MoS2 Nanocomposites for Water Remediation of Hexavalent Chromium

Water pollution has becoming an increasingly serious issue, and it has attracted a significant amount of attention from scholars. Here, in order remove heavy metal hexavalent chromium (Cr (VI)) from wastewater, graphitic carbon nitride (g-C3N4) was modified with molybdenum disulfide (MoS2) at different mass ratios via an ultrasonic method to synthesize g-C3N4/MoS2 (CNM) nanocomposites as photocatalysts. The nanocomposites displayed efficient photocatalytic removal of toxic hexavalent chromium (Cr (VI)) from water under UV, solar, and visible light irradiation. The CNM composite with a 1:2 g-C3N4 to MoS2 ratio achieved optimal 91% Cr (VI) removal efficiency at an initial 20 mg/L Cr (VI) concentration and pH 3 after 120 min visible light irradiation. The results showed a high pH range and good recycling stability. The g-C3N4/MoS2 nanocomposites exhibited higher performance compared to pure g-C3N4 due to the narrowed band gap of the Z-scheme heterojunction structure and effective separation of photo-generated electron-hole pairs, as evidenced by structural and optical characterization. Overall, the ultrasonic synthesis of g-C3N4/MoS2 photocatalysts shows promise as an efficient technique for enhancing heavy metal wastewater remediation under solar and visible light.

Materials Nanoarchitectonics at Dynamic Interfaces: Structure Formation and Functional Manipulation

The next step in nanotechnology is to establish a methodology to assemble new functional materials based on the knowledge of nanotechnology. This task is undertaken by nanoarchitectonics. In nanoarchitectonics, we architect functional material systems from nanounits such as atoms, molecules, and nanomaterials. In terms of the hierarchy of the structure and the harmonization of the function, the material created by nanoarchitectonics has similar characteristics to the organization of the functional structure in biosystems. Looking at actual biofunctional systems, dynamic properties and interfacial environments are key. In other words, nanoarchitectonics at dynamic interfaces is important for the production of bio-like highly functional materials systems. In this review paper, nanoarchitectonics at dynamic interfaces will be discussed, looking at recent typical examples. In particular, the basic topics of "molecular manipulation, arrangement, and assembly" and "material production" will be discussed in the first two sections. Then, in the following section, "fullerene assembly: from zero-dimensional unit to advanced materials", we will discuss how various functional structures can be created from the very basic nanounit, the fullerene. The above examples demonstrate the versatile possibilities of architectonics at dynamic interfaces. In the last section, these tendencies will be summarized, and future directions will be discussed.

Tunable CO2-to-syngas conversion via strong electronic coupling in S-scheme ZnGa2O4/g-C3N4 photocatalysts

The conversion of CO2 into syngas, a mixture of CO and H2, via photocatalytic reduction, is a promising approach towards achieving a sustainable carbon economy. However, the evolution of highly adjustable syngas, particularly without the use of sacrifice reagents or additional cocatalysts, remains a significant challenge. In this study, a step-scheme (S-scheme) 0D ZnGa2O4 nanodots (∼7 nm) rooted g-C3N4 nanosheets (denoted as ZnGa2O4/C3N4) heterojunction photocatalyst was synthesized vis a facial in-situ growth strategy for efficient CO2-to-syngas conversion. Both experimental and theoretical studies have demonstrated that the polymeric nature of g-C3N4 and highly distributed ZnGa2O4 nanodots synergistically contribute to a strong interaction between metal oxide and C3N4 support. Furthermore, the desirable S-scheme heterojunction in ZnGa2O4/C3N4 efficiently promotes charge separation, enabling strong photoredox ability. As a result, the S-scheme ZnGa2O4/C3N4 exhibited remarkable activity and selectivity in photochemical conversion of CO2 into syngas, with a syngas production rate of up to 103.3 μ mol g-1 h-1, even in the absence of sacrificial agents and cocatalyst. Impressively, the CO/H2 ratio of syngas can be tunable within a wide range from 1:4 to 2:1. This work exemplifies the effectiveness of a meticulously designed S-scheme heterojunction photocatalyst for CO2-to-syngas conversion with adjustable composition, thus paving the way for new possibilities in sustainable energy conversion and utilization.

Synthesis, Structural Characterization, Hirschfeld Surface Analysis and Photocatalytic CO2 Reduction Activity of a New Dinuclear Gd(III) Complex with 6-Phenylpyridine-2-Carboxylic Acid and 1,10-Phenanthroline Ligands

A new dinuclear Gd(III) complex was synthesized and named [Gd2(L)4(Phen)2(H2O)2(DMF)2]·2H2O·2Cl (1). Here, L is the 6-phenylpyridine-2-carboxylate anion, Phen represents 1,10-phenanthroline, DMF is called N,N-dimethylformamide, and Cl- is the chloride anion, which is characterized by IR and single crystal X-ray diffraction analysis. The structural analysis reveals that complex (1) is a cation-anion complex, and each Gd(III) ion is eight-coordinated with four O atoms (O1, O5, O2a, O4a, or O1a, O2, O4, O5a) of four different bidentate L ligands, two O atoms (O6, or O6a) of DMF molecules, two N atoms (N1, N2, or N1a, N2a) of Phen ligands, and two O atoms (O3 or O3a) of coordinated water molecules. Complex (1) forms the three-dimensional π-π stacking network structure with cavities occupied by chloride anions and uncoordinated water molecules. The Hirschfeld surface of the complex (1) shows that the H···H contacts represented the largest contribution (48.5%) to the Hirschfeld surface, followed by C···H/H···C and O···H/H···O contacts with contributions of 27.2% and 6.0%, respectively. To understand the electronic structure of the complex (1), the DFT calculations have been performed. The photocatalytic CO2 reduction activity shows complex (1) has excellent catalytic activity with yields of 22.1 μmol/g (CO) and 6.0 μmol/g (CH4) after three hours. And the selectivity of CO can achieve 78.5%.

g-C3N4/Ag@AgCl with Z-scheme heterojunction and Ag electron bridge for enhanced photocatalytic degradation of tetracycline wastewater

Building Z-scheme heterojunctions with an electron bridge is a favored function for increasing photocatalytic activity. A facile approach for preparing g-C3N4/Ag@AgCl ternary heterojunctions by co-precipitation and photoreduction was established in this work. First, via co-precipitation, AgCl was modified on the surface of g-C3N4 to create a broad contact area between AgCl and g-C3N4. The AgCl is then reduced to Ag via an in-situ photoreduction technique, resulting in the formation of a ternary composite. The experimental results showed that when g-C3N4 modified 25% of the Ag@AgCl, that is, g-C3N4/Ag@AgCl-25 had the best photocatalytic performance, 94.9% of TC was degraded within 240 min, and the reaction rate to TC was 0.1214 min-1, which was 4.49 times and 8.12 times higher than that of g-C3N4 and Ag/AgCl, respectively. The excellent photocatalytic performance of g-C3N4/Ag@AgCl is attributed to the LSPR effect of Ag NPs and O-doping g-C3N4, which broadens the absorbance performance of g-C3N4, the establishment of Z-type heterojunctions between AgCl NPs and g-C3N4 NSs and Ag NPs as an electron transport bridge accelerate the photogenerated electrons transfer between AgCl and g-C3N4.

Phosphorus-Doped Hollow Tubular g-C3N4 for Enhanced Photocatalytic CO2 Reduction

Photocatalytic CO2 reduction is a tactic for solving the environmental pollution caused by greenhouse gases. Herein, NH4H2PO4 was added as a phosphorus source in the process of the hydrothermal treatment of melamine for the first time, and phosphorus-doped hollow tubular g-C3N4 (x-P-HCN) was fabricated and used for photocatalytic CO2 reduction. Here, 1.0-P-HCN exhibited the largest CO production rate of 9.00 μmol·g-1·h-1, which was 10.22 times higher than that of bulk g-C3N4. After doping with phosphorus, the light absorption range, the CO2 adsorption capacity, and the specific surface area of the 1.0-P-HCN sample were greatly improved. In addition, the separation of photogenerated electron-hole pairs was enhanced. Furthermore, the phosphorus-doped g-C3N4 effectively activated the CO2 adsorbed on the surface of phosphorus-doped g-C3N4 photocatalysts, which greatly enhanced the CO production rate of photocatalytic CO2 reduction over that of g-C3N4.

Photocatalytic CO2 Conversion into Solar Fuels Using Carbon-Based Materials-A Review

Carbon materials with elusive 0D, 1D, 2D, and 3D nanostructures and high surface area provide certain emerging applications in electrocatalytic and photocatalytic CO₂ utilization. Since carbon possesses high electrical conductivity, it expels the photogenerated electrons from the catalytic surface and can tune the photocatalytic activity in the visible-light region. However, the photocatalytic efficiency of pristine carbon is comparatively low due to the high recombination of photogenerated carriers. Thus, supporting carbon materials, such as graphene, CNTs (Carbon nanotubes), g-C₃N₄, MWCNs (Multiwall carbon nanotubes), conducting polymers, and its other simpler forms like activated carbon, nanofibers, nanosheets, and nanoparticles, are usually combined with other metal and non-metal nanocomposites to increase the CO₂ absorption and conversion. In addition, carbon-based materials with transition metals and organometallic complexes are also commonly used as photocatalysts for CO₂ reduction. This review focuses on developing efficient carbon-based nanomaterials for the photoconversion of CO₂ into solar fuels. It is concluded that MWCNs are one of the most used materials as supporting materials for CO₂ reduction. Due to the multi-layered morphology, multiple reflections will occur within the layers, thus enhancing light harvesting. In particular, stacked nanostructured hollow sphere morphologies can also help the metal doping from corroding.

Photocatalysts for a sustainable future: Innovations in large-scale environmental and energy applications

The growing environmental and energy crises have prompted researchers to seek new solutions, including large-scale photocatalytic environmental remediation and the production of solar hydrogen using photocatalytic materials. To achieve this goal, scientists have developed numerous photocatalysts with high efficiency and stability. However, the large-scale application of photocatalytic systems under real-world conditions is still limited. These limitations arise at every step, including the large-scale synthesis and deposition of photocatalyst particles on a solid support, and the development of an optimal design with high mass transfer and efficient photon absorption. The purpose of this article is to provide a detailed description of the primary challenges and potential solutions encountered in scaling up photocatalytic systems for use in large-scale water and air purification and solar hydrogen production. Additionally, based on a review of current pilot developments, we draw conclusions and make comparisons regarding the main operating parameters that affect performance, as well as propose strategies for future research.

Retrospective insights into recent MXene-based catalysts for CO2 electro/photoreduction: how far have we gone?

The electro/photocatalytic CO₂ reduction reaction (CO₂RR) is a long-term avenue toward synthesizing renewable fuels and value-added chemicals, as well as addressing the global energy crisis and environmental challenges. As a result, current research studies have focused on investigating new materials and implementing numerous fabrication approaches to increase the catalytic performances of electro/photocatalysts toward the CO₂RR. MXenes, also known as 2D transition metal carbides, nitrides, and carbonitrides, are intriguing materials with outstanding traits. Since their discovery in 2011, there has been a flurry of interest in MXenes in electrocatalysis and photocatalysis, owing to their several benefits, including high mechanical strength, tunable structure, surface functionality, high specific surface area, and remarkable electrical conductivity. Herein, this review serves as a milestone for the most recent development of MXene-based catalysts for the electrocatalytic and photocatalytic CO₂RR. The overall structure of MXenes is described, followed by a summary of several synthesis pathways classified as top-down and bottom-up approaches, including HF-etching, in situ HF-formation, electrochemical etching, and halogen etching. Additionally, the state-of-the-art development in the field of both the electrocatalytic and photocatalytic CO₂RR is systematically reviewed. Surface termination modulation and heterostructure engineering of MXene-based electro/photocatalysts, and insights into the reaction mechanism for the comprehension of the structure-performance relationship from the CO₂RR via density functional theory (DFT) have been underlined toward activity enhancement. Finally, imperative issues together with future perspectives associated with MXene-based electro/photocatalysts are proposed.

Two-dimensional heterostructures for photocatalytic CO2 reduction

The photocatalysis conversion of CO₂ into fuels has become an encouraging method to address climate and energy issues as a long-term solution. Single material suffers poor yield due to low light energy utilization and high recombination rate of photoinduced electron-hole pairs. It is an efficient approach to construct heterojunction through two or three materials to improve the photocatalytic performance. Recently, 2D-based heterojunction is getting popular for outstanding properties, such as special light collecting structure to enhance light harvest, intimate interface to facilitate charge transfer and separation, and large specific surface area to provide abundant reactive sites. Recently, some new 2D-based heterostructures materials (both structure and composition) have been developed with excellent performance. 2D materials exert structural and functional advantages in these fine composite photocatalysts. In this review, the literatures about the photocatalytic conversion of CO₂ are mainly summarized based on overall structure, interface type and material type of 2D-based heterojunction, with special attention given to the preparation, characterization, structural advantages and reaction mechanism of novel 2D-based heterojunction. This work is in hope of offering a basis for designing improved composite photocatalyst for CO₂ photoreduction.

Biomass Nanoarchitectonics for Supercapacitor Applications

Nanoarchitectonics integrates nanotechnology with numerous scientific disciplines to create innovative and novel functional materials from nano-units (atoms, molecules, and nanomaterials). The objective of nanoarchitectonics concept is to develop functional materials and systems with rationally architected functional units. This paper explores the progress and potential of this field using biomass nanoarchitectonics for supercapacitor applications as examples of energetic materials and devices. Strategic design of nanoporous carbons that exhibit ultra-high surface area and hierarchically pore architectures comprising micro- and mesopore structure and controlled pore size distributions are of great significance in energy-related applications, including in high-performance supercapacitors, lithium-ion batteries, and fuel cells. Agricultural wastes or natural biomass are lignocellulosic materials and are excellent carbon sources for the preparation of hierarchically porous carbons with an ultra-high surface area that are attractive materials in high-performance supercapacitor applications due to high electrical and ion conduction, extreme porosity, and exceptional chemical and thermal stability. In this review, we will focus on the latest advancements in the fabrication of hierarchical porous carbon materials from different biomass by chemical activation method. Particularly, the importance of biomass-derived ultra-high surface area porous carbons, hierarchical architectures with interconnected pores in high-energy storage, and high-performance supercapacitors applications will be discussed. Finally, the current challenges and outlook for the further improvement of carbon materials derived from biomass or agricultural wastes in the advancements of supercapacitor devices will be discussed.

MXene Nanosheets Induce Efficient Iron Selenide Active Sites to Boost the Electrocatalytic Hydrogen Evolution Reaction

Along with the widespread utilization of hydrogen energy, the rise of highly active hydrogen evolution electrocatalysts with affordable costs presently becomes a substantial crux of this emerging domain. In this work, we demonstrate a feasible and convenient in situ seed-induced growth strategy for the construction of small-sized FeSe₂ nanoparticles decorated on two-dimensional (2D) superthin Ti₃C₂T_x MXene sheets (FeSe₂/Ti₃C₂T_x) through a manipulated bottom-up synthetic procedure. By virtue of the distinctive 0D/2D heterostructures, abundant exposed surface area, well-distributed FeSe₂ catalytic centers, strong surface electronic coupling, and high electrical conductivity, the resultant FeSe₂/Ti₃C₂T_x nanoarchitectures are endowed with a superior electrocatalytic hydrogen evolution capacity including a competitive onset potential of 89 mV, a favorable Tafel slope of 78 mV dec^-1, and a long-period stability, significantly better than that of the pristine FeSe₂ and Ti₃C₂T_x catalysts.

A Comprehensive Review on Graphitic Carbon Nitride for Carbon Dioxide Photoreduction

Inspired by natural photosynthesis, harnessing the wide range of natural solar energy and utilizing appropriate semiconductor-based catalysts to convert carbon dioxide into beneficial energy species, for example, CO, CH₄ , HCOOH, and CH₃ COH have been shown to be a sustainable and more environmentally friendly approach. Graphitic carbon nitride (g-C₃ N₄ ) has been regarded as a highly effective photocatalyst for the CO₂ reduction reaction, owing to its cost-effectiveness, high thermal and chemical stability, visible light absorption capability, and low toxicity. However, weaker electrical conductivity, fast recombination rate, smaller visible light absorption window, and reduced surface area make this catalytic material unsuitable for commercial photocatalytic applications. Therefore, certain procedures, including elemental doping, structural modulation, functional group adjustment of g-C₃ N₄ , the addition of metal complex motif, and others, may be used to improve its photocatalytic activity towards effective CO₂ reduction. This review has investigated the scientific community's perspectives on synthetic pathways and material optimization approaches used to increase the selectivity and efficiency of the g-C₃ N₄ -based hybrid structures, as well as their benefits and drawbacks on photocatalytic CO₂ reduction. Finally, the review concludes a comparative discussion and presents a promising picture of the future scope of the improvements.

Selective Reduction of CO2 on Ti2C(OH)2 MXene through Spontaneous Crossing of Transition States

Direct reduction of gas-phase CO₂ to renewable fuels and chemical feedstock without any external energy source or rare-metal catalyst is one of the foremost challenges. Here, using density functional theory and ab initio molecular dynamics (AIMD) simulations, we predict Ti₂C(OH)₂ MXene as an efficient electron-coupled proton donor exhibiting simultaneously high reactivity and selectivity for CO₂ reduction reaction (CRR) by yielding valuable chemicals, formate, and formic acid. This is caused by CO₂ spontaneously crossing the activation barrier involved in the formation of multiple intermediates. Metallic Ti₂C(OH)₂ contains easily donatable protons on the surface and high-energy electrons near the Fermi level that leads to its high reactivity. High selectivity arises from low activation barrier for CRR as predicted by proposed mechanistic interpretations. Furthermore, H vacancies generated during the product formation can be replenished by exposure to moisture, ensuring the uninterrupted formation of the products. Our study provides a single-step solution for CRR to valuable chemicals without necessitating the expensive electrochemical or low-efficiency photochemical cells and hence is of immense interest for recycling the carbon.

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.

Molecule-to-Material-to-Bio Nanoarchitectonics with Biomedical Fullerene Nanoparticles

Nanoarchitectonics integrates nanotechnology with various other fields, with the goal of creating functional material systems from nanoscale units such as atoms, molecules, and nanomaterials. The concept bears strong similarities to the processes and functions seen in biological systems. Therefore, it is natural for materials designed through nanoarchitectonics to truly shine in bio-related applications. In this review, we present an overview of recent work exemplifying how nanoarchitectonics relates to biology and how it is being applied in biomedical research. First, we present nanoscale interactions being studied in basic biology and how they parallel nanoarchitectonics concepts. Then, we overview the state-of-the-art in biomedical applications pursuant to the nanoarchitectonics framework. On this basis, we take a deep dive into a particular building-block material frequently seen in nanoarchitectonics approaches: fullerene. We take a closer look at recent research on fullerene nanoparticles, paying special attention to biomedical applications in biosensing, gene delivery, and radical scavenging. With these subjects, we aim to illustrate the power of nanomaterials and biomimetic nanoarchitectonics when applied to bio-related applications, and we offer some considerations for future perspectives.

Recent Research Progress in the Structure, Fabrication, and Application of MXene-Based Heterostructures

Two-dimensional (2D) materials have received increasing attention in the scientific research community owing to their unique structure, which has endowed them with unparalleled properties and significant application potential. However, the expansion of the applications of an individual 2D material is often limited by some inherent drawbacks. Therefore, many researchers are now turning their attention to combine different 2D materials, making the so-called 2D heterostructures. Heterostructures can integrate the merits of each component and achieve a complementary performance far beyond a single part. MXene, as an emerging family of 2D nanomaterials, exhibits excellent electrochemical, electronic, optical, and mechanical properties. MXene-based heterostructures have already been demonstrated in applications such as supercapacitors, sensors, batteries, and photocatalysts. Nowadays, increasing research attention is attracted onto MXene-based heterostructures, while there is less effort spent to summarize the current research status. In this paper, the recent research progress of MXene-based heterostructures is reviewed, focusing on the structure, common preparation methods, and applications in supercapacitors, sensors, batteries, and photocatalysts. The main challenges and future prospects of MXene-based heterostructures are also discussed to provide valuable information for the researchers involved in the field.

Black phosphorus coupled bismuth chloride oxide nanocomposites for efficient photocatalytic CO2 reduction

Photocatalytic CO2 reduction to useful CO and CH4 is significantly boosted by black phosphorus (BP) coupled bismuth oxychloride (BiOCl) nanocomposites, presenting an efficient and reliable approach to green and sustainable solar energy conversion.

One-step fabrication and photocatalytic performance of sea urchin-like CuO/ZnO heterostructures

Sea urchin-like hierarchical p-CuO/n-ZnO heterostructures were fabricated through one-step chemical bath deposition method without any surfactant or heat treatment. The morphologies and crystal structures of the obtained CuO/ZnO heterostructures were...

In situ construction of a C3N5 nanosheet/Bi2WO6 nanodot S-scheme heterojunction with enhanced structural defects for the efficient photocatalytic removal of tetracycline and Cr(vi)

A novel 2D/0D C3N5/Bi2WO6 S-scheme heterojunction with enhanced structural defects has been designed for the efficient elimination of pharmaceutical antibiotics and Cr(vi).