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Dye-sensitized system holds great potential for the development of visible-light-responsive photocatalysts not only because it can enhance the light absorption and charge separation efficiency of the systems but also because it can tune the band structure of catalysts. Herein, two-dimensional (2D) Fe-MOF nanosheets (Fe-MNS) with a LUMO potential of 0.11 V (vs. RHE) was prepared. Interestingly, it has been found that when the 2D Fe-MNS catalyst was functionalized with visible-light-responsive [Ru(bpy)]32+ as a dye-sensitizer, the electrons from the [Ru(bpy)]32+ can effectively inject into the 2D Fe-MNS, which resulted in a negative shift of the LUMO potential of the 2D Fe-MNS to −0.15 V (vs. RHE). Consequently, the [Ru(bpy)]32+/Fe-MNS catalytic system exhibits a sound photocatalytic CO2-to-CO activity of 1120 μmol g-1h−1 under visible-light-irradiation. The photocatalytic CO production was further ameliorated by regulating the electronic structure of the 2D Fe-MNS by doping Co ions, achieving a remarkable photocatalytic activity of 1637 μmol g-1h−1. This work further supports that the dye-sensitized system is an auspicious strategy worth exploring with different catalysts for the development of visible-light-responsive photocatalytic systems.

Researches on environmentally friendly semiconductor photocatalysts for efficient photocatalytic hydrogen evolution have important practical significance. Here, using first-principles calculations, the CeO2(111)/hBN heterojunction was conceived. The influence of the interface effect on the structural, electronic and optical properties of the heterojunction was investigated in detail. The band gap of the heterojunction is smaller than the two individual components and forms a type-II heterojunction, improving the photocatalytic activity. Furthermore, by doping two C atoms, the band gap of heterojunction was further narrowed. Both the oxidation and reduction potential of CeO2(111)/hBN heterojunction meet the requirements of water splitting and has certain advantages over other photocatalysts in the ability for photocatalytic hydrogen evolution. The study revealed the possible mechanism of CeO2(111) and hBN monolayers compositing to facilitate photocatalysis and hydrogen evolution ability, which may provide a possible reference direction for the practical design of more high-quality semiconductor photocatalysts.

Photoreduction of CO2 to valuable fuels with semiconductor photocatalysts is a good solution to the problems of global warming and energy crisis. Creation of hybrid nanomaterials with hierarchical and/or heterojunction structures is beneficial to develop efficient photocatalysts for CO2 reduction. Herein we present a convenient method to obtain a hybrid photocatalyst consisting of MnS and In2S3 nanosheets with assembled hierarchical structures through using Mn2+-loaded MIL-68(In) submicro-rods as templates. Owing to the dispersive Mn2+ and In3+ ions in templates, numerous small p-n heterojunctions of MnS/In2S3 could be simultaneously produced in each hierarchical particle. The p-type MnS and n-type In2S3 with an original type II band alignment can create a stronger built-in electric field after the formation of p-n heterojunctions, which is favorable for charge separation and migration to catalyst surface. The prepared MnS/In2S3 heterojunctions show an 4-fold higher photocatalytic activity toward CO2 reduction than pristine MnS and In2S3. The MnS/In2S3 hierarchical structures were well characterized and their working mechanism was explored. This work demonstrates a facile strategy to create efficient hybrid photocatalysts with both hierarchical structures and p-n heterojunctions for photocatalytic applications.

Developing suitable catalysts capable of receiving injected electrons and possessing active sites for hydrogen evolution reaction (HER) is the key to building an efficient dye-sensitized system for hydrogen production. Fe3S4 is generally regarded as an inferior HER catalyst among the metal sulfide family, mainly due to its weak surface adsorption toward H atoms. In this work, we demonstrate a facile metal-organic framework-derived method to synthesize uniform Fe3S4 nanorods and active them for HER by Ni doping. Our experimental results and theoretical calculations reveal that Ni doping can greatly modify the electronic structure of Fe3S4 nanorods, improving their electron conductivity and optimizing their surface adsorption energy toward H atoms. Sensitized by a commercial organic dye (eosin-Y), 1%Ni-doped Fe3S4 nanorods display a high H2 production rate of 3240 μmol gcat-1 h-1 with an apparent quantum yield of 12% under 500 nm wavelength, which is significantly higher than that of pristine Fe3S4 and even higher than that of 1% Pt-deposited Fe3S4. The working mechanism of this dye-sensitized system is explored, and the effect of Ni-doping concentration has been studied. This work presents a facile strategy to synthesize metal-doped sulfide nanocatalysts with greatly enhanced activity toward photocatalytic H2 production.

As a class of new emerged semiconductors, MHPs exhibit many excellent photoelectronic properties, which are superior to most conventional semiconductor nanocrystals (NCs). Particularly, MHPs have received extensive attention and brought new opportunities for the development of photocatalysis. Over the past few years, numerous efforts have been made to design and prepare MHP-based materials for a wide range of applications in photocatalysis, ranging from photocatalytic H2 generation, photocatalytic CO2 reduction, photocatalytic organic synthesis and pollutant degradation. In this review, recent advances in the development of MHP-based materials are summarized from the standpoint of photocatalysis. A brief outlook of this field has been proposed to point out some important challenges and possible solutions. This review suggests that the new family of MHP photocatalysts provide a new paradigm in efficient artificial photosynthesis.

Photocatalytic reduction of CO2 into value-added chemical fuels is an appealing approach to address energy crisis and global warming. CsPbBr3 quantum dots (QDs) are good candidates for CO2 reduction because of their excellent photoelectric properties, including high molar extinction coefficient, low exciton binding energy, and defect tolerance. However, the pristine CsPbBr3 QDs generally have low photocatalytic performance mainly due to dominant charge recombination and lack of efficient catalytic sites for CO2 adsorption/activation. Herein, we report a new photocatalytic system, in which CsPbBr3 QDs are coupled with covalent triazine frameworks (CTFs) for visible-light-driven CO2 reduction. In this hybrid photocatalytic system, the robust triazine rings and periodical pore structures of CTFs promote the charge separation in CsPbBr3 and endow them with strong CO2 adsorption/activation capacity. The resulting photocatalytic system exhibits excellent photocatalytic activity towards CO2 reduction. This work presents a new photocatalytic system based on CTFs and perovskite QDs for visible-light-driven CO2 reduction, which highlights the potential of perovskite-based photocatalysts for solar fuel applications.

Using ion doping to engineer sulfur vacancies over metal sulfides is an effective method to improve photocatalytic properties, such vacancies form the center of the electron-captured state to promote the separation and transfer of photogenerated carriers. In this research, Yb/Er co-doped bulk Cd0.5Zn0.5S (CZS) was fabricated by a one-step simple hydrothermal process, and used for evaluating the catalytic activity for aquatic hydrogen production under visible light irradiation. The results showed that the Cd0.5Zn0.5S:Yb(15%), Er obtained exhibited a higher efficient photocatalytic activity of hydrogen evolution, in which the efficiency of Cd0.5Zn0.5S:Yb(15%), Er (422.0 μmol g−1 h−1) was 2.7 times higher than that of bare Cd0.5Zn0.5S (154.7 μmol g−1 h−1). This can be attributed to the augmented active surface area, the broadened spectral absorption of visible light and the facilitation of the separated efficiency of the photogenerated carriers. This finding provides a simple way to activate the metal-chalcogenides with S-vacancies for optimizing the photocatalytic performance.

Photocatalytic CO2 reduction is an appealing approach to convert solar energy into high value-added chemicals. All-inorganic CsPbBr3 quantum dots (QDs) have emerged as a promising photocatalyst for reducing CO2. However, pristine CsPbBr3 has a low catalytic performance, mainly due to severe charge recombination. Herein, a 0D/2D heterojunction of CsPbBr3 QDs/Bi2WO6 nanosheet (CPB/BWO) photocatalysts is fabricated for photocatalytic CO2 reduction. The CPB/BWO photocatalyst achieves excellent photocatalytic performance: the total yield of CH4/CO is 503 μmol g-1, nearly 9.5 times higher than the pristine CsPbBr3. The CPB/BWO heterojunction also exhibits much-improved stability during photocatalytic reactions. On the basis of various characterization techniques, our investigations verified a direct Z-scheme charge migration mechanism between CsPbBr3 QDs and Bi2WO6 nanosheets. The improved photocatalytic performance is originated from the high spatial separation of photoexcited charge carriers in CPB/BWO, which can also preserve strong individual redox abilities of two components. This work reports an efficient direct Z-scheme heterojunction photocatalytic system based on metal halide perovskites. The novel strategy we proposed may bring up new opportunities for the development of metal halide perovskite photocatalysts with greatly enhanced activities.

Photocatalytic CO2 reduction is a promising technology to mitigate global warming and enrich energy supply. Metal–organic frameworks (MOFs) are prospective photocatalysts for CO2 reduction, but severe charge recombination and limited visible light response largely restrain their applications. As carbon dots (CDs) can act as both electron receptors and photosensitizers, here we propose to develop CD-hybridized MOF photocatalysts for improving their activity for CO2 reduction. In particular, because of the small size of CDs, we have managed to encapsulate CDs inside MOF particles and found that these CD@MOFs exhibit hugely improved photocatalytic activity compared with CD-decorated MOFs or pristine MOFs. Our investigations suggest that placing small CD cocatalysts near the internal metal–oxo clusters of MOFs can help efficient charge transfer and separation in the hybrid photocatalysts, due to the formation of many small heterojunctions among MOFs. The developed CD-hybridized MOF catalysts are characterized in detail and their working mechanism is explored. This work may demonstrate a novel strategy to develop MOF-based hybrid photocatalysts with enhanced photocatalytic activity.

Harvesting solar energy to convert carbon dioxide (CO2) into fossil fuels shows great promise to solve the current global problems of energy crisis and climate change. To achieve this goal, it is desirable to develop efficient catalysts with visible light response to cater for the solar spectrum. CdTe QDs are ideal candidates for absorbing visible light, but it is difficult to directly perform CO2 reduction due to the lack of effective catalytic sites. Herein, we report a strategy for the activation of mercaptopropionic acid (MPA)-capped CdTe QDs for visible-light-driven CO2 reduction, in which iron ions (Fe2+) are immobilized onto CdTe QDs using L-cysteine as a bridging ligand (CdTe-b-Fe). This ligand bridging strategy can immobilize Fe2+ ions on the surface of CdTe QDs as catalytic sites, and these catalytic sites can be conveniently adjusted by directly adding different types or numbers of metal ions. In addition to effectively immobilizing catalytic sites, the bridging ligands can also provide a pathway for electron transport between CdTe QDs and the catalytic sites. The CdTe-b-Fe QD system based on the ligand bridging strategy exhibits excellent catalytic properties: the yield of CH4/CO (two products together) is 126 μmol g−1 h−1, and the selectivity for carbon-based products approaches 98%. This work presents a facile strategy for immobilizing catalytic sites on QDs and provides a platform for designing efficient visible-light driven catalysts for CO2 reduction.

Splitting water into hydrogen (H2) with sunlight is an appealing approach towards alleviating the fossil fuel crisis. However, as one of the most promising light harvesters, colloidal quantum dots (QDs) generally exhibit low photocatalytic activity towards H2 evolution because of the lack of catalytic sites on their surface. Many researchers have focused on activating QDs by anchoring metal complexes on their surface, in which the photoexcited electrons may transfer from the QDs to the metal centres via the organic ligands. These bulky organic ligands usually have poor electrical conductivity and chemical instability, thereby causing high charge recombination and low durability in these QDs/metal complex catalysts. To address these issues, we herein report the doping of cadmium telluride (CdTe) QDs with nickel ions (Ni2+), achieving a remarkable H2 generation rate without the use of co-catalysts. The formation rate of H2 exceeded 27.3 mmol/g/h under visible light irradiation, which is approximately 110-fold higher than that of pristine CdTe QDs. This doping strategy provides a versatile route to reduce protons to H2 with a turnover number of 13,650 in terms of Ni and confer superior durability on the CdTe QDs.

Fe-based metal-organic frameworks (MOFs) have shown promising applications in photocatalysis, yet they are incapable of photocatalytic H2 production due to their inappropriate conduction band (CB) position and large overpotential for H2 evolution. Herein, we present a facile strategy enabling the photocatalytic H2 production over Fe-based MOFs through dye sensitization. A combination of characterization techniques with theoretical simulation reveals that dye sensitization can effectively inject energetic electrons into Fe-MOFs and elevate their quasi-Fermi level under light irradiation, overcoming the surface overpotential for H2 production from water. Furthermore, deposition of Pt nanoparticles on Fe-MOFs can lower the overpotential for H2 evolution toward further enhanced photocatalytic activity. This work provides insights into MOF band structure engineering at electronic level, and proves a concept that harnesses MOF materials for targeted photocatalytic applications they are originally not fit for.

Quantum dots (QDs), a class of promising candidates for harvesting visible light, generally exhibit low activity and selectivity towards photocatalytic CO2 reduction. Functionalizing QDs with metal complexes (or metal cations through ligands) is a widely used strategy for improving their catalytic activity; however, the resulting systems still suffer from low selectivity and stability in CO2 reduction. Herein, we report that doping CdS QDs with transition-metal sites can overcome these limitations and provide a system that enables highly selective photocatalytic reactions of CO2 with H2 O (100 % selectivity to CO and CH4 ), with excellent durability over 60 h. Doping Ni sites into the CdS lattice leads to effective trapping of photoexcited electrons at surface catalytic sites and substantial suppression of H2 evolution. The method reported here can be extended to various transition-metal sites, and offers new opportunities for exploring QD-based earth-abundant photocatalysts.

Converting CO2 into high-valued chemicals with sunlight is regarded as a promising way to solve the impending energy and environmental crisis. Development of efficient photocatalysts with suitable energy band gap, high stability and favorable structure is thus of very importance. Herein, a novel hierarchical Bi2WO6 photocatalyst assembled by Bi2WO6 nanosheets with a hollow and rod-shaped appearance has been developed via a facile hydrothermal process. Interestingly, we found that the hydrolysis of Bi(NO3)3 in water can produce solid Bi6O5(OH)3(NO3)5·3H2O microrods which can be transformed to hollow-hierarchical Bi2WO6 nanosheets by virtue of the Kirkendall effect. The developed Bi2WO6 nanosheets exhibit a 58 times higher specific surface area than that of bulk Bi2WO6 and a remarkable enhancement in electrochemical performance such as photocurrent and charge transfer. As a result, the hollow-hierarchical structured Bi2WO6 photocatalysts achieve a high CH4 yield of 2.6 μmol g−1 h−1, 8 times higher than that of bulk Bi2WO6. Moreover, the developed photocatalysts exhibit a high stability during the recycling experiments. This work may present a new strategy to attain hierarchical structured photocatalysts with high activity and stability toward CO2 reduction.

Inspired by the distinct advantages of BiOCl(001) ultrathin nanosheets being rich in oxygen vacancies (VO) and metal nanoparticles (NPs) with unique surface activity for the adsorption-activation of alcohols, metal-decorated BiOCl(001) ultrathin nanosheets were expected to exhibit enhanced photocatalysis for the selective oxidation of aromatic alcohols. Herein, a small quantity (1.5 wt%) of Au and Pd NPs were loaded on ultrathin BiOCl(001) nanosheets by photodeposition to obtain Au–BiOCl and Pd–BiOCl photocatalysts, respectively. Among the various photocatalysts including BiOCl ultrathin nanosheets, light-irradiated BiOCl ultrathin nanosheets, and metal-decorated BiOCl ultrathin nanosheets, the Pd–BiOCl sample displayed the highest photocatalytic activity for the oxidation of aromatic alcohols to the corresponding aldehydes under ambient conditions. According to a series of experimental analyses as well as the insights from the calculations, the enhanced photocatalysis of Pd–BiOCl was attributed to the remarkable interface cooperation by the electronic coupling between Pd and the BiOCl(001) surface, where the abundant VO sites of BiOCl(001) ultrathin nanosheets and the surface activity of Pd NPs synergistically promote the adsorption-activation of O2 and alcohol molecules as well as facilitating the separation and transfer of photogenerated carriers. These findings highlight the synergistic effect of the metal–semiconductor interface on the photocatalytic oxidation of organic compounds and shed some light on the rational design of highly efficient photocatalysts for selective conversion processes with environmentally benign oxidants like O2.

Upconversion (UC) NaYF4:Yb,Tm nanocrystals (NCs) are capable of converting low-energy near-infrared (NIR) photons to high-energy ultraviolet (UV) and visible (Vis) photons. Integration of NaYF4:Yb,Tm with graphitic carbon nitride (g-C3N4) can extend the spectral response of g-C3N4 to the NIR range. However, photocatalytic activity of NaYF4:Yb,Tm/g-C3N4 is still severely limited by the high recombination rate of photo-generated (PG) electrons and holes (e–/h+) in the g-C3N4. Herein, we report a facile approach to fabricate a ternary nanocomposite consisting of NaYF4:Yb,Tm, TiO2 and g-C3N4. When NaYF4:Yb,Tm NCs were coated with a TiO2 shell and sequentially assembled with g-C3N4 nanosheets (NSs), a semiconductor heterojunction can be fabricated on the UC particles. The as-prepared nanocomposites possess an enhanced photocatalytic activity under Vis and/or NIR lights due to the formation of heterojunction and UC effect. The ternary nanocomposites have been characterized in detail and their photocatalytic mechanism is proposed. Such kind of ternary nanocomposites may provide a new scenario for the design and synthesis of composite photocatalysts for efficiently utilizing the Vis/NIR lights in environmental remedy.

Photocatalytic reduction of CO2 into high value-added CH4 is a promising solution for energy and environmental crises. Integrating semiconductors with cocatalysts can improve the activities for photocatalytic CO2 reduction; however, most metal cocatalysts mainly produce CO and H2. Herein, we report a cocatalyst hydridation approach for significantly enhancing the photocatalytic reduction of CO2 into CH4. Hydriding Pd cocatalysts into PdH0.43 played a dual role in performance enhancement. As revealed by our isotopic labeling experiments, the PdH0.43 hydride cocatalysts reduced H2 evolution, which suppressed the H2 production and facilitated the conversion of the CO intermediate into the final product: CH4. Meanwhile, hydridation promoted the electron trapping on the cocatalysts, improving the charge separation. This approach increased the photocatalytic selectivity in CH4 production from 3.2% to 63.6% on Pd{100} and from 15.6% to 73.4% on Pd{111}. The results provide insights into photocatalytic mechanism studies and introduce new opportunities for designing materials towards photocatalytic CO2 conversion.

2D/2D hBN/g-C3N4 nanocomposites with good photocatalytic activity have been successfully prepared, and fortunately defected 2D material heterojunction opens up new possibilities for high-efficiency photocatalysts. However, its photocatalytic performance and mechanism in splitting water have not been thoroughly explored. Herein, using the state-of-theart TDHF-HSE06 method, 2D/2D hBN/g-C3N4 nanocomposites with different defected types were discussed in detail, including C atoms doping and natural point vacancies. We demonstrate that the defect-induced Z-scheme vdW heterojunction is a key for excellent photocatalytic performance. Compared to perfect hBN/g-C3N4, the defected hBN/g-C3N4 heterojunctions have stronger interfacial interaction with more than 20 times of charge transfer. And it even has full visible-light response due to the suitable band gap width. More importantly, the Z-scheme band edge potentials have perfect redox capacity for water splitting at both PH = 0 and 7. The findings not only explain the existing experimental phenomena, but also provide new insights into the design of high-efficiency metal-free photocatalysts.

ZnO is one of the most promising materials for both photocatalytic and antibacterial applications, but its wide bandgap requires the excitation of UV light which limits their applications under visible and NIR bands. Herein, we demonstrate a facile approach to synthesize core-shell-shell hybrid nanoparticles consisting of hexagonal NaYF4:Yb,Tm, amorphous SiO2 and wurtzite ZnO. The upconversion nanocrystals are used as the core seeds and sequentially coated with an insulting shell and a semiconductor layer. Such hybrid nanoparticles can efficiently utilize the NIR light through the upconverting process, and display notable photocatalytic performance and antibacterial activity under NIR irradiation. The developed NaYF4:Yb,Tm@SiO2@ZnO nanoparticles are characterized with TEM, XRD, EDS, XPS and PL spectra, and their working mechanism is also elucidated.

Fe-Based MOFs can serve as low cost, stable, eco-friendly and visible light-driven photocatalysts, exhibiting promising applications in a broad range of fields. However, the present modification or semiconductor-coupling routes are still unable to extend their light response to the NIR region. Herein we present a microwave-assisted method to prepare MIL-53(Fe) octahedra with uniform concave facets. This unique structural geometry enables MIL-53(Fe) to trap upconversion nanocrystals (UCNPs) on their concave surface with a stable morphology. The developed MIL-53(Fe)/UCNP composites exhibit remarkable photocatalytic activity under NIR light and enhanced performance under Vis-NIR light. Through modifying the organic linkers with amino groups, both light absorption and utilization of upconverted emission of the composites can be enhanced, showing an improved activity. The formation and working mechanisms of the MOF/UCNP composite photocatalysts are also explored.

The construction of a p-n heterojunction is an efficient strategy to resolve the limited light absorption and serious charge-carrier recombination in semiconductors and enhance the photocatalytic activity. However, the promotion effect is greatly limited by poor interfacial charge transfer efficiency as well as reduced redox ability of charge carriers. In this work, we demonstrate that the embedding of metal Pd into the interface between n-type C3N4 and p-type Cu2O can further enhance the interfacial charge transfer and increase the redox ability of charge carriers through the design of the C3N4-Pd-Cu2O stack nanostructure. The embedded Pd nanocubes in the stack structure not only trap the charge carriers from the semiconductors in promoting the electron-hole separation but also act as a Z-scheme "bridge" in keeping the strong reduction/oxidation ability of the electrons/holes for surface reactions. Furthermore, Pd nanocubes also increase the bonding strength between the two semiconductors. Enabled by this unique design, the hydrogen evolution achieved is dramatically higher than that of its counterpart C3N4-Cu2O structure without Pd embedding. The apparent quantum efficiency (AQE) is 0.9% at 420 nm for the designed C3N4-Pd-Cu2O. This work highlights the rational interfacial design of heterojunctions for enhanced photocatalytic performance.

Graphitic carbon nitride (g-C3N4) coupled with Bi2WO6 is a promising Type II heterojunction, but it is still difficult to obtain uniform nanocomposites of these materials with the present assembly methods. Here we employ g-C3N4 nanosheets saturated with Bi3+ ions to provide numerous and widespread nucleation sites for the growth of Bi2WO6 nanocrystals. As a result, g-C3N4 nanosheets loaded with fine and controllable amount of Bi2WO6 nanocrystals are produced. The g-C3N4/Bi2WO6 nanocomposites exhibit significantly enhanced photocatalytic activity for RhB degradation under visible-light irradiation. Particularly, the g-C3N4/70 % Bi2WO6 nanocomposite achieves the highest photocatalytic activity, and the average rate constant is almost 5 and 9 times higher than those of bare g-C3N4 and Bi2WO6, respectively. Moreover, the composite exhibits high photocatalytic stability in cycling tests.

Utilization of visible and near-infrared light has always been the pursuit of photocatalysis research. In this article, an approach is developed to integrate dual plasmonic nanostructures with TiO2 semiconductor nanosheets for photocatalytic hydrogen production in visible and near-infrared spectral regions. Specifically, the Au nanocubes and nanocages used in this work can harvest visible and near-infrared light, respectively, and generate and inject hot electrons into TiO2 . Meanwhile, Pd nanocubes that can trap the energetic electrons from TiO2 and efficiently participate in the hydrogen evolution reaction are employed as co-catalysts for improved catalytic activity. Enabled by this unique integration design, the hydrogen production rate achieved is dramatically higher than those of its counterpart structures. This work represents a step toward the rational design of semiconductor-metal hybrid structures for broad-spectrum photocatalysis.

Photocatalytic degradation of environmental pollutants by using semiconductor-based photocatalysts offers great potential for remediation of toxic chemicals. For an economical and eco-friendly method to eliminate hexavalent chromium (Cr(VI)), favourable catalysts own high efficiency, stability and capability of harvesting light. Combination of metal with semiconductor is a promising route to improve the photocatalytic performance for Cr(VI) reduction. Herein, well-dispersed platinum (Pt) nanocubes (NCs) were synthesized by a facile one-step hydrothermal method with poly- l -lysine (PLL) as the growth-directing agent, followed by their uniform dispersion on graphitic carbon nitride (g-C3N4). Their morphology, crystal structure, chemical composition, and formation mechanism were mainly characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The hybrid nanocomposite was further explored for photocatalytic reduction of Cr(VI) to trivalent chromium (Cr(III)) under visible light at room temperature, by using formic acid (HCOOH) as a reducing agent, showing great improvement in photocatalytic activity and reusability, outperforming the referenced g-C3N4 and home-made Pt black/g-C3N4 catalysts. The effects of various experimental parameters and the proposed mechanism are discussed in detail.

The combination of a metal with a semiconductor is a promising route to improve the solar-to-chemical conversion efficiency of photocatalysts. In this article, ultrathin Pd nanosheets are integrated with semiconductor TiO2 nanosheets for photocatalytic hydrogen evolution, which acts as a cocatalyst and plasmonic agent in ultraviolet and visible-near-infrared spectral regions, respectively. Owing to the unique two-dimensional (2D) nanostructure, the Pd nanosheet cocatalyst realizes the large TiO2–Pd interfacial area for electron transfer as well as a large Pd exposed area for reduction reactions, while the plasmonic Pd nanosheets offer strong vis-NIR light absorption for “hot” electron production as well as a large interfacial area for “hot” electron injection. As a result, the Pd nanosheets achieve improved photocatalytic activity in comparison with three-dimensional Pd nanotetrahedrons under both light irradiations. This work underlines the importance in choosing a suitable shape of metal in the surface and interface design of semiconductor–metal hybrid photocatalysts as well as the advantages of 2D metal nanostructures in realizing high photocatalytic performance.

In this work, we described a facile one-pot hydrothermal process developed to synthesize CdS/C core–shell nanospheres successfully. The as-prepared CdS/C core–shell nanospheres are with 100 nm in diameter and the amorphous carbon shell is with several nanometers in thickness. The phase, morphology and structures of the samples were investigated by X-ray power diffraction (XRD) analyses, field-emission scanning electron microscopy (FESEM, JEOL-6700F) and transmission electron microscopy (TEM, JEOL 3010); respectively. The as-prepared CdS/C core–shell nanospheres showed enhanced photocatalytic properties and photostability compared to the single counterpart of CdS nanospheres owing to the efficiently separation of photogenerated electrons (e − ) and holes (h + ) derived from the photocatalyst. In addition, the as-prepared CdS/C core–shell nanospheres might find wide application in wastewater treatment, solar cells, lithium ion batteries, etc.

Decreasing the shell thickness of TiO2 hollow spheres is a promising route to achieve an overall enhanced photocatalytic performance. However, in traditional synthetic approaches, the thin shell can not guarantee the structural stability of the TiO2 hollow spheres in the following calcination process to achieve a high degree of crystallinity. In this paper, ultrathin porous TiO2 hollow spheres with good structural stability, high degree of crystallinity as well as in small grain size were prepared through a novel etching and reconstruction route using amorphous SiO2/TiO2 hollow spheres as precursor. With hot water as etchant, the removal of SiO2 leads to the reconstruction of TiO2 hollow spheres and receiving a thinner and thinner shell. Such thin shell enables the exposure of more catalytic active sites of TiO2 nanocrystals and the improved photogenerated charge transfer and separation. Meanwhile, the residual SiO2 on the TiO2 shell protects the TiO2 nanocrystals from growing larger during high-temperature calcinations. The as-obtained ultrathin porous TiO2 hollow spheres exhibited enhanced photocatalytic activity in hydrogen production from water in comparison with those with thicker shell.

Carbon-coated nickel-doped-ZnO nanorods (Ni/ZnO@C NRs) are successfully prepared for the purpose of improving the visible-light photocatalytic performance of ZnO by expanding the absorption in the visible-light region and increasing the separation efficiency of photogenerated charges. The physicochemical properties of the catalysts were characterized using SEM, TEM, XRD, and Raman, FT-IR, UV-vis diffuse reflectance and PL spectra. The results indicated that nickel ions substituted for Zn2+ in the lattice of ZnO, whereas all the carbon was uniformly coated on the surface of the nanorod photocatalysts. Among the Ni/ZnO@C samples with different ion-doping levels and carbon coating content, the 1.0 mol% Ni/ZnO@C-3 sample possessing a carbon layer thickness of 3.8 nm exhibited a higher visible light activity and synergistic effects of the nickel and carbon, which were responsible for improving the photocatalytic activity. By using the hydrothermal carbon layer as a sacrificial template, nanovoid core–shell structured Ni/ZnO@void@SiO2 was obtained through subsequent silica coating and calcination reactions. Its porous shell could adsorb dye molecules from the bulk solution and accumulate them in the void space where the Ni/ZnO core is more accessible than for the bare Ni/ZnO nanorods in bulk solution, meanwhile the nanovoid structure could also avoid shielding of the catalyst-active sites by the outer layer, which leads to a significant photocatalytic activity enhancement. In addition, antibacterial studies of Ni/ZnO@void@SiO2 under sunlight irradiation were performed against Escherichia coli. This nanovoid photocatalyst exhibited high inhibition of the Gram-negative bacterial strain with co-action of the surface adsorption of the mesoporous SiO2 and the strong oxidation abilities of the formed reactive oxygen species.

The combination of upconversion nanocrystals with a wide-bandgap semiconductor is an efficient strategy to develop near-infrared (NIR)-responsive photocatalysts. The photocatalytic activity of the hybrid structures is greatly determined by the efficiency of the energy transfer on the interface between upconversion nanocrystals and the semiconductor. In this work, we demonstrate the interface design of a NaYF4:Yb,Tm–BiOCl hybrid structure based on the choice of suitable BiOCl facets in depositing NaYF4:Yb,Tm upconversion nanocrystals. It was found that the selective deposition of NaYF4:Yb,Tm nanocrystals on the BiOCl(110) facet can greatly enhance the photocatalytic performance in dye degradation compared with the sample with NaYF4:Yb,Tm nanocrystals loaded on the BiOCl(001) facet. Two effects were believed to contribute to this enhancement: (1) a stronger UV emission absorption ability of the BiOCl(110) facet from NaYF4:Yb,Tm in generating more photo-induced charge carriers resulted from the narrower bandgap; (2) a shorter diffusion distance of photogenerated charge carriers to the BiOCl(110) reactive facet for surface catalytic reactions owing to the spatial charge separation between different facets. This work highlights the rational interfacial design of an upconversion nanocrystal–semiconductor hybrid structure for enhanced energy transfer in photocatalysis.

High-quality hexagonal NaYF4:Yb,Tm upconversion nanocrystals (UCNs) prepared in organic solutions display uniform sizes and strong UC emissions, but they possess a hydrophobic surface which hinders combining them with various semiconductor nanocrystals (NCs) to form a hybrid NIR-activated photocatalyst. Herein we present a facile approach to modify hydrophobic UCNs with a uniform carbon layer and enable them with hydrophilicity and surface functionalization. The carbon shell provides a good substrate for enriching with metal ions and in situ generation of CdS nanoclusters on the particle surface which can utilize both the upconverted UV and visible emissions. The developed NaYF4:Yb,Tm@C@CdS nanoparticles are characterized with TEM, SEM, XRD, PL and UV-Vis spectra and their formation mechanism is elucidated. The products display good photocatalytic activity under visible light and obviously enhanced performance under Vis-NIR light, due to the efficient utilization of UC emissions and the strong adsorption capacity of the carbon shell. The working mechanism of the hybrid photocatalysts is also proposed.

Development of TiO2-based photocatalysts capable of utilizing NIR light is very important for practical applications using the solar spectrum. The combination of upconversion nanocrystals (UCNs) with TiO2 is a promising route for activation of photocatalysts under NIR irradiation. Here we propose integration of dually sensitized UCNs with N-doped TiO2 with a core–shell–shell structure. In such composite photocatalysts, the core–shell UCNs exhibit enhanced UC emissions in response to two NIR bands and all the UC emissions can be utilized by the N-TiO2 shell. The doping manner of the UCN cores and the N-doping level of the TiO2 shell both have a significant effect on the photocatalytic activity. Our results suggest that rational design of the configuration of the component materials is a feasible way to improve the photocatalytic activity of such UCN/TiO2 nanocomposites.

Development of magnetic visible-light-driven photocatalysts is desirable to the practical application of photocatalyts for collection and recycling use. Here we present a facile approach to synthesize Fe3O4@C@CdS magnetic photocatalysts which can avoid multi-step preparation process. Through one-step solvothermal carbonization of ferrocene, the produced carbon-coated Fe3O4 clusters can serve as both magnetic cores and deposition substrates for in situ generating crystalline CdS nanocrystals on them by rapid microwave irradiation. The prepared Fe3O4@C@CdS nanoparticles exhibit a uniform core–shell structure and display good photocatalytic activity and recyclability in the degradation of organic dyes. These magnetic photocatalysts may find potential application in wastewater treatment for the future environment remedy.

Surfaces and interfaces are two key parameters to maneuver the performance of photocatalytic materials, particularly for hybrid structures, in various reaction systems. In this Focus Review, we highlight the recent progress on surface and interface engineering toward designing highly efficient photocatalysts, and elucidate the fundamental principles behind the designs. We first introduce the roles of surfaces and interfaces in different models of charge kinetics—a key process determining the quantum efficiency of photocatalysis—followed by the definitions of surface and interface in basic photocatalytic architectural structures. We then outline the design rules and important parameters for surface and interface engineering, respectively. As an interplay effect, the relationships between surface and interface parameters in photocatalyst design are also presented. We further summarize the synthetic methods for surface and interface control. Finally, we discuss the challenges and opportunities for photocatalysis research in terms of surface and interface engineering.

Core–shell nanostructures are of great scientific and technological importance owing to their enhanced physical and chemical properties. In this work, we report a facile synthesis of unusual Ag/TiO2 (B) hierarchical core–shell nanowires with 200 nm in diameter and tens of micrometers in length for the first time. The hierarchical core–shell nanowires of Ag/TiO2 have been achieved from silver nitrate, tetrabutyl orthotitanate and ethylene glycol via a synergistic soft-hard template method. Each of the hierarchical core–shell nanowires of Ag/TiO2 is comprised of Ag nanowires with 50–70 nm in diameter and sheath comprised of ultrathin nanosheets of monoclinic β-TiO2 with several nanometers in thickness and preferential exposure of (010) facet. Several experimental observations illustrate that temperature and amount of tetrabutyl orthotitanate play key roles in formation of this kind of hierarchical core–shell nanostructures. As expected, the hierarchical core–shell nanostructures exhibited enhanced photocatalytic performance on degradation towards RhB. In particular, the as-prepared Ag/TiO2 core–shell nanowires exhibit superior, durable bacteriostatic and bactericidal properties.

Graphitic (g-) C3N4 is a promising visible light-driven photocatatalyst but it has a narrow absorption in the solar spectrum. To broaden its light utilization, here we present a strategy to integrate upconversion nanocrystals into g-C3N4 nanosheets by electrostatic assembly. This hybrid photocatalyst can be activated under both visible and near-infrared (NIR) lights, showing improved photocatalytic activity in the full solar spectrum. Phase, morphology and activity of this composite photocatalyst are characterized and its working mechanism is also proposed.

Because of the limited penetration depth of visible light that generally excites most of the available photosensitizers (PSs), conventional photodynamic therapy (PDT) is limited to the treatment of superficial and flat lesions. Recently, the application of deep penetrating near-infrared (NIR) light excitable upconversion nanoparticles (UCNs) in conjunction with PDT has shown to have clear potential in the treatment of solid tumors due to its ability to penetrate thick tissue. However, various constructs developed so far have certain limitations such as poor or unstable PS loading, reducing their therapeutic efficacy and limiting their application to solution or cell-based studies. In this work, we present a method to fabricate uniform core-shell structured nanoconstruct with a thin layer of photocatalyst or PS-titanium dioxide (TiO2) stably coated on individual UCN core. Our design allows controllable and highly reproducible PS loading, preventing any leakage of PS compared to previously developed nanoconstructs, thus ensuring repeatable PDT results. Further surface modification of the developed nanoconstructs with polyethylene glycol (PEG) rendered them biocompatible, demonstrating good therapeutic efficacy both in vitro and in vivo.

Synthesis of N-doped TiO2 hollow spheres with a small grain size, large surface area and high degree of crystallinity is favorable to achieve an overall high photocatalytic activity. But traditional synthetic approaches generally involve many tedious steps and are time-consuming. Here we present a facile method to synthesize N-doped TiO2 hollow spheres using organic silane-doped silica nanoparticles as templates. The organic–inorganic silica can be simultaneously etched during the deposition of TiO2 shell to create a thin silica layer on the TiO2 surface. Such a thin silica layer can efficiently protect the TiO2 nanocrystals from growing larger during high-temperature calcination. At the same time, the organic silane can serve as a nitrogen source to be doped in the TiO2 shell. The developed silica-protected and N-doped TiO2 hollow spheres can be directly employed as photocatalysts without SiO2 etching and show obvious light utilization in both UV and visible bands.

Nickel-doped zinc oxide hollow nanospheres have been synthesized using a simple solvothermal approach through a morphological transformation driven by a localized Ostwald ripening process. The saturation magnetization of the system shows that the materials have only a short-range magnetic ordering in them. Based on the visible-light photocatalytic experiment, we could confirm that, with a high doping content (10 mol%), the doping accompanied with increased recombination which reduced the energy of photoinduced electron leading to suppressed photocatalytic activity. Changing reaction parameters, i.e. the mixed reactant concentration, doping content, and different solvents, Zn1−xNixO powders exhibited the elongated prismatic form with sharp tips, quasi-spherical structure, and hexagonal-based polyhedron, respectively. The photocatalytic results demonstrate that different crystal growth orientations, specific surface areas, particle size distributions, and doping levels have strong influences on the photocatalytic activity performances. Among the samples, hexagonal-based polyhedrons have the best photodegradation efficiency standing on higher fraction of exposed polar facets, larger specific surface area, as well as an optimal doping level. The 1 mol% nickel content showed the best photocatalytic activities among the nickel-doped zinc oxide samples.

Combination of upconversion nanocrystals (UCNs) with CeO2 is a decent choice to construct NIR-activated photocatalysts for utilizing the NIR light in the solar spectrum. Herein we present a facile approach to deposit a CeO2 layer with controllable thickness on the plate-shaped NaYF4:Yb,Tm UCNs. The developed core–shell nanocomposites display obvious photocatalytic activity under the NIR light and exhibit enhanced activity under the full solar spectrum. For enhancing the separation of photogenerated electrons and holes on the CeO2 surface, we sequentially coat a ZnO shell on the nanocomposites so as to form a heterojunction structure for achieving a better activity. The developed hybrid photocatalysts have been characterized with TEM, SEM, PL, etc., and the working mechanism of such UCN-semiconductor heterojunction photocatalysts has been proposed.

α-Fe 2 O 3 nanoparticles-decorated ZnO nanorod-assembled hollow spheres were successfully synthesized by a simple acetone-assisted impregnation deposition. SEM images showed a uniform distribution of α-Fe 2 O 3 nanoparticles not only on the surfaces of ZnO spheres but also inside pores of ZnO parallel aligned nanorods. The α-Fe 2 O 3 /ZnO binary semiconductor composites exhibited a superior visible-light photocatalytic activity for degradation of rhodamine B (RhB) as compared with pure ZnO spheres. The enhancement was attributed to stronger visible light absorption ability and effective photogenerated charge separation of α-Fe 2 O 3 /ZnO composites.

Titania (TiO2) has been explored as a potential drug in eradicating cancer by virtue of its photocatalytic property to generate reactive oxygen species (ROS) under UV irradiation. Its clinical application, however, has been hampered by the tissue penetration depth limit of the UV light needed for its activation. The use of ‘invisible’ near-infrared (NIR) light affords greater tissue penetration depth because most tissues are ‘transparent’ to NIR light. Here, we uniformly coated TiO2 to a nanometer-sized light transducer that can upconvert highly penetrating NIR light to the activation absorption spectrum of TiO2 at UV range. Under NIR excitation, photoinduced TiO2 by the upconverted UV light results in the generation of more than one type of ROS that was stably produced under an appropriate storage condition. The amount of ROS produced was also effective in killing cancer cells in vitro, thus suggesting its potential in overcoming the current penetration depth limit.

We demonstrate a facile method to directly coat a TiO2 layer on hydrophobic NaYF4:Yb,Tm upconversion nanocrystals. Through modifying the hydrophobic nanocrystals with a surfactant layer, a conventional sol–gel route can be applied to them for TiO2 deposition. The prepared β-NaYF4:Yb,Tm@TiO2 particles show obvious photocatalytic activity under near-infrared light as well as ultraviolet light. Based on the success in preparing upconversion cores with different sizes and subsequent TiO2 coating, we have systematically investigated the effect of core sizes on their photocatalytic performance. The results suggest that upconversion fluorescence of the core and surface of the shell both have a great effect on their photocatalytic activities. A moderate core size is thus preferred, due to the competition between these two effects.

We have developed a facile method to synthesize upconversion YF3:Yb,Tm nanocrystals in ethylene glycol. These nanocrystals exhibit an assembly structure with a peanut-like appearance. A layer of TiO2 shell can be facilely coated on the YF3:Yb,Tm nanocrystals via a sol–gel process and crystallized through annealing. The developed YF3:Tb,Tm@TiO2 particles show good photocatalytic activity under the UV band and work better in the UV/NIR band of a Xe lamp, as the core particles can efficiently upconvert NIR light into UV one.

Development of MOF-based photocatalysts is intriguing research due to their structural flexibility and tremendous catalytic sites, whereas most MOFs only can take use of UV/visible light and lack of response to NIR light. Herein, we present a facile approach to integrate upconversion nanoparticles (UCNPs) with MOF to build a NIR-responsive composite photocatalyst. The MOF shell with controllable thickness can be grown on the UCNPs, thus exhibiting tunable photocatalytic activities under NIR irradiation. Furthermore, we extend visible absorption of the MOF shell by adding −NH2 groups so that the composite photocatalysts have a better utilization of UC emissions and sunlight to improve their activities. The developed composite photocatalysts have been characterized by XRD, TEM, PL, etc., and their photocatalytic performances were systematically explored. The formation and working mechanism of the composite photocatalysts were also elucidated.

Recent advances in photocatalysis highlight the important role of cocatalysts in improving the solar-to-chemical conversion efficiency for various reactions, such as water splitting and CO2 reduction reactions. Given that cocatalysts play two important roles, in charge trapping and surface reactions, the rational material design of cocatalysts would be an effective route in pursuing their maximum contribution to the performance of photocatalysts. In this review, we aim to outline the recent progress of surface and interface design in cocatalysts for photocatalytic water splitting and CO2 reduction. We first introduce the surface design of cocatalysts, which enables the enhancement of specific water splitting or CO2 reduction reactions through surface parameter (e.g., the composition, facets and phases) adjustments. We then present key parameters for designing the interface between photocatalyst and cocatalyst, which offer a set of versatile options for tuning the charge transfer to the cocatalyst. Taken together, the surface and interface of cocatalysts may have synergetic effects on the photocatalytic performance, which are discussed to provide guidance for simultaneously tailoring surface and interface parameters. Finally, we summarize the challenges and opportunities for the surface and interface design of cocatalysts for the efficient production of solar fuels.

The facet-engineered surface and interface design for photocatalytic materials has been proven as a versatile approach to enhance their photocatalytic performance. This review article encompasses some recent advances in the facet engineering that has been performed to control the surface of mono-component semiconductor systems and to design the surface and interface structures of multi-component heterostructures toward photocatalytic applications. The review begins with some key points which should receive attention in the facet engineering on photocatalytic materials. We then discuss the synthetic approaches to achieve the facet control associated with the surface and interface design. In the following section, the facet-engineered surface design on mono-component photocatalytic materials is introduced, which forms a basis for the discussion on more complex systems. Subsequently, we elucidate the facet-engineered surface and interface design of multi-component photocatalytic materials. Finally, the existing challenges and future prospects are discussed.

This manuscript describes the accurate coating of CdS nanoparticles on the surface of colloidal carbon spheres by a facile two-step, microwave-assisted method and the studies on the photocatalytic activity of the C@CdS core-shell spheres. For the coating of CdS nanoparticles, cadmium ions were incorporated into the hydrophilic shell of colloidal carbon spheres and reacted with an introduced sulfur source under a microwave field to obtain the C@CdS hybrid spheres. Using this process, the as-prepared hybrid structures preserved the good dispersity and uniformity of initial carbon spheres, and the thickness of the CdS nanoparticles shell could be varied or controlled by the irradiation time. A photoluminescence spectrum showed that the C@CdS hybrid spheres feature a broad green emission at around 494 nm (λ(ex) = 337 nm). Additionally, CdS nanospheres were successfully prepared in aqueous solution via a microwave-assisted route, and the effect of irradiation time on the products was also investigated. The studies of the photocatalytic property demonstrate that these fabricated functional hybrid structures evinced a higher photocatalytic degradation activity when exposed to visible light irradiation than that of CdS nanospheres under the same conditions.