Photoexcited Charge Carriers Research Articles

An effective CuO/Bi2WO6 heterostructured photocatalyst: Analyzing a charge-transfer mechanism for the enhanced visible-light-driven photocatalytic degradation of tetracycline and organic pollutants

Over the past few years, industrial pollution has had a negative impact on aquatic life by releasing significant amounts of hazardous chemicals into the ecosystem. Therefore, it is imperative to develop photocatalytic materials with good photocatalytic activity and easy separation. Photocatalytic degradation has been employed for the removal of such contaminants using binary hybrid nanocomposites as photocatalysts. In the present study, binary CuO/Bi2WO6 (CuBW) nanocomposites with different loadings of Bi2WO6 (~5, 10, and 15 mg) were successfully constructed using a simple hydrothermal method and used as a potential photocatalyst for the degradation of tetracycline (TC) and methylene blue (MB) under visible-light irradiation. The structure, surface morphology, and optical properties were studied to investigate the formation of the heterostructure. Among the prepared samples, the CuBW nanocomposite containing the optimum content of Bi2WO6 (~10 mg) exhibited superior activity toward the photocatalytic degradation of TC (97.72%) in 75 min and MB (99.43%) in 45 min under visible-light illumination. Radical trapping experiments suggested that holes and •OH radicals were the dominant reactive species during the photocatalytic process. The photoelectrochemical results also confirmed the improved separation and transfer of electron-hole pairs at the interface of Bi2WO6 and CuO. Our results demonstrate that the binary CuO/Bi2WO6 nanocomposite has significant potential applications in the field of photocatalysis due to its enhanced separation of the photoexcited charge carriers and strong synergistic interactions.

Insight into the Real Efficacy of Graphene for Enhancing Photocatalytic Efficiency: A Case Study on CVD Graphene-TiO2 Composites

Construction of graphene-based composites has been a popular theme in solar energy harvesting and conversion, yet the understanding of the real efficacy of graphene for enhancing photocatalytic efficiency is hampered by the gap of physicochemical properties between the defined graphene and the graphene used in research laboratories. Here, we purposely synthesize a high-quality chemical vapor deposition graphene (CVDG) as a model material to integrate with TiO2, which demonstrates that photocatalytic performance can be greatly improved by controlling the quality of graphene. Under the same reaction conditions, the as-prepared CVDG-TiO2 displays a 26.2-times and 10-times higher photocatalytic hydrogen evolution activity than bare TiO2 and its counterpart, reduced graphene oxide (RGO)-TiO2, respectively. Experimental characterization reveals that the few-layer CVDG with a low defect density is able to better unleash the excellent electrical conductivity potential of graphene, by which the separation and lifetime of photoexcited charge carriers of graphene-TiO2 could be improved more efficiently. The research highlights the significant effect of the quality of graphene for the construction of more efficient semiconductor-graphene composites, which is anticipated to inform ongoing efforts on exploiting high-quality graphene to advance solar energy harvesting and conversion.

Synergistic effects of Tin sulfide Nitrogen-doped titania Nanobelt-Modified graphitic carbon nitride nanosheets with outstanding photocatalytic activity

Designing efficient ternary nanostructures is a feasible approach for energy production under simulated solar irradiation. In this study, excellent photoexcited charge carrier separation and enhanced visible-light response were achieved with nitrogen-doped titania nanobelts (N-TNBs), whose 1D geometry facilitated the fabrication of a heterostructure with SnS2 on the surface of graphitic carbon nitride (g-C3N4). We established the design of SnS2@N-TNB and SnS2@N-TNB/g-C3N4 heterostructures by in situ hydrothermal and ultrasonication processes, and achieved commendable simulated solar light driven photocatalytic H2 generation. UV–vis diffuse reflectance spectroscopy analysis revealed a red shift in the absorption spectra of the SnS2@N-TNB and SnS2@N-TNB/g-C3N4 samples. The H2 produced via SnS2@N-TNB-10/g-C3N4 (6730.8 µmol/g/h) was 2.6 times higher than that produced by SnS2@N-TNB (2515.1 µmol/g/h), and 299 times higher than that produced by N-TNB (22.5 µmol/g/h). The improved photocatalytic H2 production was attributed to the maximum interface contact between SnS2@N-TNB and g-C3N4, and to the improved visible-light absorption and effective charge-carrier separation. Therefore, the present study provides novel insights for combining the advantages of ternary materials to improve the conversion of solar energy to H2 fuel.

ZnO/CdS/CuS heterostructure: A suitable candidate for applications in visible-light photocatalysis

To eliminate the coloured-elements/dyes from effluents, ZnO based photocatalysts are significantly effective. Using simple low temperature aqueous solution process ZnO/CdS/CuS ternary heterostructure has been developed, wherein CdS and CuS nanoparticles are embedded onto the surface of micron-sized ZnO hexagonal disks, the morphology and chemical composition of which are determined by X-ray diffraction, transmission electron spectroscopy and X-ray photoelectron spectroscopy. The CdS and CuS nanoparticles on the ZnO surface play crucial roles in substantial reduction of the optical band gap that facilitates in a significant visible light photocatalysis characteristics of the heterostructure. An enlarged surface area of the heterostructure contributes increased number of reactive sites for dye adsorption. Besides the synergistic effect, the optimized band structures of ZnO, CdS and CuS strategically influence on the effective electron-hole separation and transfer. Efficient photocatalytic dye degradation is accomplished via formation of the superoxide radicals (O2•−) by the CB-electrons and the hydroxyl radicals (•OH) by the VB-holes. For ZnO/CdS/CuS heterostructures superior photocatalytic activity with the highest degradation rate constants ‘k’, ~0.0152 min−1 for RhB dye and 0.0217 min−1 for MO dye are obtained via strategically impeding the recombination of photoexcited charge carriers by proper band alignment among different components of the heterostructure.

CeO2 supported Zn1-xMnxS (x: 0.025, 0.05, 0.075 and 0.10) catalyst for photoremoval of rhodamine B dye

Present work provides a detailed study of enhanced photocatalytic performance of CeO2 coupled Mn-doped ZnS nanoparticles. In a systematic study, undoped and Mn− doped (2.5, 5, 7.5 and 10 mol%) ZnS nanoparticles were synthesized using co-precipitation method. Then, using synthesized samples, heterostructure samples (ZnS/CeO2) were prepared by hydrothermal route. Successful incorporation of Mn ions in ZnS lattice was determined by X-ray diffraction, transmission electron microscopy and Fourier-transform infrared spectroscopy. Optical spectroscopies revealed the associated optical modifications because of Mn-doping and confirmed CeO2 attachment. The specific surface area calculated from N2 sorption isotherms suggested the mesoporous structure of the samples. Rhodamine B (RhB) dye was used to understand the structural modifications of both components for the photocatalytic performance under different radiations. It was observed that hydroxyl radicals (OH∙) were responsible for photo-oxidation of RhB molecule with excellent photostability of synthesized heterostructure sample under UV–visible illumination. To prove photocatalytic activity of catalysts under visible light, additional experiments with the use of vancomycin antibiotic, which do not absorb visible light, were performed. Though Mn doping improves the recombination rate of charge carriers of host ZnS, the attachment of CeO2, not even reduces the optical bandgap (red shift) but contributes to better separation of the photo-excited charge carriers in heterostructure catalysts.

Revealing the transfer mechanisms of photogenerated charge carriers over g-C3N4/ZnIn2S4 composite: A model study for photocatalytic oxidation of aromatic alcohols with visible light

Semiconductor photocatalysis as an alternative technology has received extensive attention for addressing the worldwide energy and environment issues. However, it is still a great challenge and imperative to profoundly understand the migration mechanisms for achieving the complete utilization of photoexcited charge carriers. In this paper, a series of g-C3N4/ZnIn2S4 heterojunction composites were fabricated by thermal polycondensation and solvothermal methods and then thoroughly characterized by a range of techniques. Photocatalytic selective oxidation of aromatic alcohols to corresponding aldehydes with O2 under visible light irradiation was introduced as a model reaction system to evaluate the photocatalytic performance of the as-prepared samples. The results exhibit that when the main constituent of photocatalyst is ZnIn2S4, the transfer of the photogenerated charge carriers adopts a band-band mechanism in g-C3N4/ZnIn2S4 heterojunction composite. However, when the main constituent of photocatalyst is g-C3N4, the transfer of the photogenerated charge carriers adopts a Z-scheme mechanism. Therefore, the different compositions of the composite samples lead to the different electronic conductivities and then affect the direction of the built-in electric field in the relative p-n junction, finally causing the different transfer mechanisms of the photogenerated charge carriers for g-C3N4/ZnIn2S4 composite samples.

Operating Temperature of Nonfullerene Acceptor‐Based Bulk Heterojunction Organic Solar Cells

A comprehensive study of the operating temperature () of three nonfullerene (NF) acceptor‐based bulk heterojunction organic solar cells (BHJ OSCs), two conventional (OSC1 and OSC3) and one inverted (OSC2) structure, is presented. A quantitative analysis of the thermal power generated by photon absorption in transport layers and electrodes, thermalization of photoexcited charge carriers, tail‐state recombination, and resistive heating is conducted. For all three OSCs, the dependence of operating temperature on the voltage is simulated and it is found that OSC1 and OSC2 operate at about 320 K and OSC3 at 319 K. It is also found that the thermal power generated due to thermalization (PT) and absorption in other than the active layer () in OSC3 are smaller than those in both OSC1 and OSC2 but the thermal power generated due to the resistive heating (PR) is larger in OSC3 than in OSC1 and OSC2, leading to the net power absorbed in the active layer of OSC3 being higher than that in OSC1 and OSC2. Thus, although the operating temperature of all three cells remains in the range from 320 to 321 K, OSC3 shows a better photovoltaic performance.

Anatomy of a Natural Sunlight Driven CdS/CoTiO3/ZnO Ternary Photocatalyst for Efficient Optical Properties and Removal of Reactive Orange 30

ZnO as a promising photocatalyst has gained much attention for the removal of organic pollutants from water. However, the main drawbacks of the relatively low photocatalytic activity and high recombination rate of photoexcited electron-hole pairs restrict its potential applications. Promoting the spatial separation of photoexcited charge carriers is of paramount significance for photocatalysis because the difference in the band positions makes the potential gradient at the composite boundary. In this work, binary CdS/ZnO and CoTiO3/ZnO are first prepared by dispersion method and then decorated with ZnO particles to construct CdS/CoTiO3/ZnO ternary composites. For this reason, the CdS/CoTiO3/ZnO ternary composites was effectively designed and analyzed for the crystalline structure, light absorption, photoexcitation behavior and surface morphological properties by X-ray diffraction, diffuse reflectance UV/visible absorption spectroscopy, photoluminescence spectroscopy and scanning electron micrograph respectively. The photocatalytic activity was examined by degradation of the dye solution spectrophotometrically. The results of photocatalytic degradation indicated that the CdS/CoTiO3/ZnO ternary composites are much higher than those of bare CdS, CoTiO3, ZnO and any binary composites such as CoTiO3/ZnO and ZnO/CdS. The enhanced activity could be attributed to the drop electron transfer from CdS to ZnO to CoTiO3 through the interfacial potential gradient in the ternary hybrid conduction bands. The enhanced electron transfer of CdS/CoTiO3/ZnO ternary composites was also applicable to degrade other reactive dyes.

Fabrication of size-controlled hierarchical ZnS@ZnIn2S4 heterostructured cages for enhanced gas-phase CO2 photoreduction

Designing and constructing advanced heterojunction architectures are desirable for boosting CO2 photoreduction performance of semiconductor photocatalysts. Herein, we have prepared hierarchical ZnS@ZnIn2S4 core-shell cages with controlled particle sizes using sequential synthesis of Zeolitic imidazolate (ZIF-8) polyhedrons, ZnS cages, and ZnIn2S4 nanosheets on the ZnS polyhedron cages. ZIF-8 polyhedrons are firstly synthesized by a liquid-phase approach. The subsequent sulfidation of the ZIF-8 polyhedrons results in the formation of ZnS polyhedron cages, which act as substrates for fabricating ZnS@ZnIn2S4 core-shell cages by growing ZnIn2S4 nanosheets. The size of ZnS cages can be tuned to optimize CO2 photoreduction performance of hierarchical ZnS@ZnIn2S4 core-shell cages. The synergy of the unique hierarchical core-shell cage-like structure and heterojunction composition endows the hybrid catalyst high incident light utilization, abundant active sites, and effective separation of photoexcited charge carriers. Benefiting from these advantages, the optimized hierarchical ZnS@ZnIn2S4 core-shell cages exhibit enhanced performance for CO2 photoreduction with the CO yield of 87.43 μmol h−1g−1 and 84.3% selectivity, which are much superior to those of single ZnIn2S4 or ZnS. Upon Au decoration, the CO2 photoreduction performance of ZnS@ZnIn2S4 core-shell cages is further enhanced because of the Schottky junctions and surface plasmon resonance effect.

Enhancing Light Absorption and Prolonging Charge Separation in Carbon Quantum Dots via Cl-Doping for Visible-Light-Driven Photocharge-Transfer Reactions.

Limited light absorption beyond the UV region and rapid photocarrier recombination are critical impediments for the improved photocatalytic performance of carbon quantum dots (CQDs) under visible-light irradiation. Herein, we demonstrate single-step microwave-assisted syntheses of O-CQDs (typical CQDs terminated by carboxylic and hydroxyl functional groups) from a sucrose precursor and Cl-doped CQDs (Cl-CQDs) from a sucralose precursor in short reaction times and without using obligatory strong acids for Cl doping. The doping of Cl into the CQDs is observed to widen the absorption range and facilitate an enhanced separation of photoexcited charge carriers, which is confirmed by the results of optical absorption, photothermal response, and pump-probe ultrafast transient absorption spectroscopy measurements of the O-CQDs and Cl-CQDs. The photoexcited charge carriers with their longer lifetimes in Cl-CQDs enabled the quick degradation of methylene blue dye, rapid conversion of Ag+ ions to metallic Ag nanoparticles on the CQD surfaces, and reduction of GO to a well-dispersed rGO through the photoelectron transfer reactions under visible-light irradiation. The facile Cl doping strategy, hybridization of Ag nanoparticles or rGO to CQDs, and the elevated charge separation mechanism would open up new avenues in designing CQD-based materials for futuristic applications.

Effects of Crystallographic Orientation of GaAs Substrate and the Period of Plasmon Grid on THz Antenna Performance

AbstractAn alternative approach is proposed to improve the conventional (based on the low‐temperature grown GaAs and Si‐doped GaAs superlattice) photoconductive antenna (PCA) performance by modification of the planar electrodes design and crystallographic orientations of the GaAs substrate ((100) and (111)‐A). The electrode scheme design includes a combination of logarithmic spiral, bow‐tie, and plasmonic antennas and results in appearance of sharp resonant peaks, high spectral bandwidth and high signal‐to‐noise ratio, and significant enhancement of the output terahertz (THz) power. The material design leads to significant increase in the THz output power (by 6.4 in GaAs (100), by 5.6 in GaAs (111)‐A PCAs) regarding to a conventional antenna. The substrate crystallographic cut direction influences the relaxation time constant of photoexcited charge carriers being an order of magnitude smaller in the sample grown on the GaAs (111)‐A than in the one on the GaAs (100). The simulation model supports experimental results demonstrating that the optimal period of the plasmonic antenna grid providing the highest efficiency of THz radiation generation, is about 200 nm. Comparison of the THz spectra in manufactured antennas against the conventional stripline PCA shows a broadening band toward the low‐frequency region down to 0.1 THz with a resonance at 0.2 THz.

Enhanced Sunlight-Driven Reactive Species Generation via Polarization Field in Nanopiezoelectric Heterostructures.

Although it is established that the force-induced electric polarization field of piezoelectric semiconductors can be used to tune the transfer rate of photoexcited charge carriers, there is still a lack of successful strategies to effectively improve the photocatalytic reactivity and solar-to-chemical conversion efficiency (SCC) of piezoelectric materials. Here, we are the first to prepare and study a kind of catalyst based on nanopiezoelectric heterostructures of LiNbO3-type ZnTiO3·TiO2 and tetragonal BaTiO3 with Pt or FeOx nanoparticle modification (i.e., ZBTO-Pt or ZBTO-FeOx) for reactive species generation. With respect to the production of •OH and •O2- radicals, higher amounts were observed in piezophotocatalysis relative to those for individual piezo- and photocatalysis. Benefiting from the charge transfer resistance decreases by the deposition of Pt and FeOx, the amounts of •OH radicals formed on ZBTO-Pt and ZBTO-FeOx were approximately 48 and 21% higher than that on isolated ZBTO during piezophotocatalysis, and for the amounts of •O2- radicals the enhancements were approximately 11 and 6%, respectively. Furthermore, the concentrations of H2O2 formed on ZBTO-Pt and ZBTO-FeOx under piezophotocatalysis reached approximately 315 and 206 μM after 100 min of reaction (and was still increasing) corresponding to 0.10 and 0.06% SCCs, respectively, which were also much higher than the concentrations and SCCs observed for piezo- and photocatalysis. The enhancements of piezophotocatalytic activities with these piezoelectric materials were related to the mechanical strain exerted on ZBTO, which generated a larger electric polarization field than those on ZnTiO3·TiO2 and BaTiO3 as analyzed by a finite element method. This high-intensity electric polarization field accelerated the separation and transportation of photoexcited charge carriers in the highly sunlight responsive nanopiezoelectric heterostructures based on ZBTO-Pt and ZBTO-FeOx.

Carrier Diffusion and Recombination Anisotropy in the MAPbI3 Single Crystal.

MAPbI3, one of the archetypical metal halide perovskites, is an exciting semiconductor for a variety of optoelectronic applications. The photoexcited charge-carrier diffusion and recombination are important metrics in optoelectronic devices. Defects in grain interiors and boundaries of MAPbI3 films cause significant nonradiative recombination energy losses. Besides defect impact, carrier diffusion and recombination anisotropy introduced by structural and electronic discrepancies related to the crystal orientation are vital topics. Here, large-sized MAPbI3 single crystals (SCs) were grown, with the (110), (112), (100), and (001) crystal planes simultaneously exposed through the adjusting ratios of PbI2 to methylammonium iodide (MAI). Such MAPbI3 SCs exhibit a weak n-type semiconductor character, and the Fermi levels of these planes were slightly different, causing a homophylic p-n junction at crystal ledges. Utilizing MAPbI3 SCs, the photoexcited carrier diffusion and recombination within the crystal planes and around the crystal ledges were investigated through time-resolved fluorescence microscope. It is revealed that both the (110) and (001) planes were facilitated to be exposed with more MAI in the growth solutions, and the photoluminescence (PL) of these planes manifesting a red-shift, longer carrier lifetime, and diffusion length compared with the (100) and (112) planes. A longer carrier diffusion length promoted photorecycling. However, excessive MAI-assisted grown MAPbI3 SCs could increase the radiative recombination. In addition, it revealed that the carrier excited within the (001) and (112) planes was inclined to diffuse toward each other and was favorable to be extracted out of the grain boundaries or crystal ledges.

Hot-Carrier Cooling in High-Quality Graphene Is Intrinsically Limited by Optical Phonons.

Many promising optoelectronic devices, such as broadband photodetectors, nonlinear frequency converters, and building blocks for data communication systems, exploit photoexcited charge carriers in graphene. For these systems, it is essential to understand the relaxation dynamics after photoexcitation. These dynamics contain a sub-100 fs thermalization phase, which occurs through carrier–carrier scattering and leads to a carrier distribution with an elevated temperature. This is followed by a picosecond cooling phase, where different phonon systems play a role: graphene acoustic and optical phonons, and substrate phonons. Here, we address the cooling pathway of two technologically relevant systems, both consisting of high-quality graphene with a mobility >10 000 cm2 V–1 s–1 and environments that do not efficiently take up electronic heat from graphene: WSe2-encapsulated graphene and suspended graphene. We study the cooling dynamics using ultrafast pump–probe spectroscopy at room temperature. Cooling via disorder-assisted acoustic phonon scattering and out-of-plane heat transfer to substrate phonons is relatively inefficient in these systems, suggesting a cooling time of tens of picoseconds. However, we observe much faster cooling, on a time scale of a few picoseconds. We attribute this to an intrinsic cooling mechanism, where carriers in the high-energy tail of the hot-carrier distribution emit optical phonons. This creates a permanent heat sink, as carriers efficiently rethermalize. We develop a macroscopic model that explains the observed dynamics, where cooling is eventually limited by optical-to-acoustic phonon coupling. These fundamental insights will guide the development of graphene-based optoelectronic devices.

LayerPCM: An implicit scheme for dielectric screening from layered substrates.

We present LayerPCM, an extension of the polarizable-continuum model coupled to real-time time-dependent density-functional theory, for an efficient and accurate description of the electrostatic interactions between molecules and multilayered dielectric substrates on which they are physisorbed. The former are modeled quantum-mechanically, while the latter are treated as polarizable continua characterized by their dielectric constants. The proposed approach is purposely designed to simulate complex hybrid heterostructures with nano-engineered substrates including a stack of anisotropic layers. LayerPCM is suitable for describing the polarization-induced renormalization of frontier energy levels of the adsorbates in the static regime. Moreover, it can be reliably applied to simulating laser-induced ultrafast dynamics of molecules through the inclusion of electric fields generated by Fresnel-reflection at the substrate. Depending on the complexity of the underlying layer structure, such reflected fields can assume non-trivial shapes and profoundly affect the dynamics of the photo-excited charge carriers in the molecule. In particular, the interaction with the substrate can give rise to strong delayed fields, which lead to interference effects resembling those of multi-pulse-based spectroscopy. The robustness of the implementation and the above-mentioned features are demonstrated with a number of examples, ranging from intuitive models to realistic systems.

Bi4O5Br2 anchored on Ti3C2 MXene with ohmic heterojunction in photocatalytic NH3 production: Insights from combined experimental and theoretical calculations

Nitrogen-to-ammonia conversion under mild conditions offers a tremendous prospect as a sustainable technology for synthesizing ammonia (NH3) in the future. In this study, we elaborately designed Bi4O5Br2/Ti3C2 heterojunction combined with electrostatic adsorption with in-situ growth to form a photocatalyst with a 2D/2D structure. This unique structure substantially improved the exposure of active edge sites for photocatalytic dinitrogen reduction reaction. Notably, Ti3C2 MXene acted as an efficient cocatalyst for the conversion of N2 to NH3 of Bi4O5Br2/Ti3C2 with a yield of 277.74 μmol g−1h−1 without the use of a sacrificial agent; this yield was five times higher than that of Bi4O5Br2. Density functional theory calculations demonstrated that the ohmic contact was at the Bi4O5Br2/Ti3C2 interface. The ohmic heterojunction could expedite the separation of spatial carriers and extraction of photoexcited charge carriers, which had outstanding reducibility to cleavage the N≡N bond. This work provides a novel strategy for designing highly efficient Bi4O5Br2-based photocatalysts through the integration of multifunctional materials. This work also offers guidance for implementing high-performance nitrogen-to-ammonia conversion by introducing interfacial modifiers.

The enhanced photocatalytic activity of ZnO nanorods/CuO nanourchins composite prepared by chemical bath precipitation

In this work, ZnO nanorods (NRs)/CuO nanourchins (NUs) were composed together to achieve the highest efficiency in methylene blue (MB) degradation. The nanocomposites were fabricated via a one-step, facile, and solution-based method named chemical bath precipitation. Crystal structures of hexagonal ZnO NRs and monoclinic CuO NUs phases were detected by X-ray diffraction (XRD) analysis, while field emission scanning electron microscopy (FESEM) confirmed the formation of ZnO NRs and CuO NUs with favorable interconnectivity. The chemical bonding stage of the Cu2+, Zn2+, and O2− were investigated with high-resolution X-ray photoelectron spectroscopy (HRXPS). Brunauer-Emmett-Teller (BET) method depicted a relatively wide pore size distribution for all the samples. Diffuse reflectance spectroscopy (DRS) demonstrated that band gap energy of ZnO NRs further narrowed by raising CuO concentration owing to the formation of the Cu(3d) energy state near the Zn(3d) valance band. Photoluminescence (PL) spectra revealed that the combination of ZnO NRs with CuO NUs significantly increased the lifetime of the photo-excited charge carriers. The ZnO/(10 mol%)CuO nanocomposite with the band gap energy of 2.9 eV and pore volume of 0.0180 cm3/g exhibited the highest efficiency and complete degradation of MB in less than 240 min. The photo-degradation kinetics of the as-prepared nanocatalyst followed a pseudo-first-order reaction model and exhibited about 12 times faster than ZnO. Finally, the photo-degradation mechanisms are proposed based on the role of reactive oxygen species and photo-generated charge carriers.

Disordered nitrogen-defect-rich porous carbon nitride photocatalyst for highly efficient H2 evolution under visible-light irradiation

Precursor types play crucial factors for synthesizing high-efficiency graphitic carbon nitrides (GCNs). Herein, biuret was employed as a new precursor to prepare a disordered nitrogen-defect-rich porous GCN (BCN). The crystallinity, structure and performance properties for BCN were explored by making systematic comparisons with other commonly available GCNs which were derived from conventional precursors under the identical conditions. Biuret could be the optimal choice for the preparation of high-performance GCN according to the reports so far. BCN not only possessed long-range atomic disordered structure, but also contained numerous nitrogen defects embedded into the in-planes of the disordered GCN networks, leading to extended visible-light absorption (absorption edge at 525 nm), improved separation of photoexcited charge carriers, and rich available reactive sites. The large surface area and high porosity of BCN also provided plenty of reactive sites. Consequently, ultrahigh photocatalytic H2 production and excellent O2 production performance were achieved for BCN, the AQY for H2 production achieved 45.5% at 420 nm, which was one of the highest values for GCN-based photocatalysts.

Interaction Promotes the Formation and Photothermal Conversion of Carbon Dots/Polydopamine Composite for Solar‐Driven Water Evaporation

AbstractCarbon dots modified with polydopamine (CDs/PDA), a low‐cost and environmentally friendly photothermal material, is prepared in this work. The results show that the polymerization of dopamine is significantly accelerated due to the interaction between CDs and dopamine. Importantly, the interaction also greatly promotes nonradiative recombination of photoexcited charge carriers, thereby enhancing the photothermal conversion performance of CDs/PDA. The obtained CDs/PDA composite shows superior photothermal evaporation efficiency in comparison with CDs and PDA owing to the enhanced light absorption, porous structure, and appropriate interaction. In addition, CDs/PDA exhibits excellent stability. These merits enable CDs/PDA show great promise in solar‐energy‐related applications.

One-step in-situ synthesis of Bi-decorated BiOBr microspheres with abundant oxygen vacancies for enhanced photocatalytic nitrogen fixation properties

The conversion of atmospheric nitrogen (N2) to ammonia (NH3) under mild conditions is quite challenging due to high stability of the triple covalent bond. Here we report that Bi-decorated BiOBr microspheres with plentiful oxygen vacancies (OVs) were successfully fabricated by one-step solvothermal strategy and used as effective photocatalysts for nitrogen fixation. The metallic Bi was reduced in-situ by glycerol and deposited on the surface of BiOBr microspheres. The synchronously generated OVs can serve as the activation center for nitrogen. Compared to pure BiOBr, Bi@BiOBr hetero-structured microspheres have higher specific surface area, superior visible-light utilization, more effective separation of photoexcited charge carriers, thus exhibiting more pronounced visible light photocatalytic N2 fixation performance. Specifically, the N2 reduction rate of the Bi@BiOBr-2 is 1350 μmol g−1 h−1, which is 11.8 times higher than pure BiOBr (114 μmol g−1 h−1). This study provides a simple and low energy consumption method for effective and stable photocatalytic N2 fixation.