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Element doping has been extensively employed to modulate the physicochemical properties of semiconductors. In this work, Se-doped CdS quantum dots (QDs) with varied Se doping level are fabricated via a solvothermal procedure. Due to the introduction of Se, the Fermi level position of CdS is elevated to a higher position, leading to the effective capture of photogenerated electrons by the trapping sites, which greatly inhibits the recombination of electron-hole pairs and thus prolong the charge carriers’ lifetime. Furthermore, due to the introduction of Se, the density of charge carriers in CdS is significantly enhanced, which is conducive to the production of more photo-generated electrons and holes. It is because of the two favorable factors that the photocatalytic performance of the resultant CdS0.9Se0.1 QDs is greatly improved with a remarkable hydrogen evolution rate of 29.12 mmol h−1 g−1 under simulated solar irradiation (320–780 nm) without any co-catalysts, which is 23.5 times that of the pristine CdS QDs under the same conditions. Moreover, the apparent quantum efficiency (AQE) over CdS0.9Se0.1 QDs reaches 27.1% at 400 nm without co-catalyst addition. This work confirms the feasibility of suppressing the recombination of electron-hole pairs by adjusting the capture level with impurity doping for exploring highly efficient photocatalysts.

Introducing co-catalyst and constructing heterostructure are two of the most promising strategies in improving the photocatalytic H2 evolution performance of semiconductors. However, it has always been a great challenge to develop a facile and low-cost system to facilitate the highly efficient synergistic effect between co-catalyst and heterostructure. Herein, co-catalyst NiS decorated ZnS/CdS heterostructure (CdS/ZnS-NiS) has been fabricated by using a facile one-pot hydrothermal procedure for the photocatalytic H2 evolution from water splitting. As a result, CdS, ZnS and NiS contact closely with each other at nano scale to assemble into fluffy porous nanocomposite, the optimized CdS/ZnS-NiS exhibits a high hydrogen evolution rate of 60.44 mmol·h-1g-1 without the addition of extra noble metal co-catalyst, which is about 22.3 times higher than that of pure CdS and much higher than that of 1% wt Pt decorated CdS/ZnS (52.36 mmol·h-1g-1). One-pot fabrication process allows the formation of intimate contacted interface between different components, contributing to the sufficient exposure of active reaction sites. Moreover, noble-metal-free co-catalyst NiS distributes uniformly in both surface and inner region of porous nanocomposite. The synergistic effect between the intimately contacted heterostructure and co-catalyst boosts the separation and utilization of photogenerated charge carriers, resulting in a dramatically enhanced H2 evolution ability. This work provides a facile pathway to uniformly introduce noble-metal-free co-catalyst in heterostructure and gives out a paradigm in constructing high active solar energy conversion system.

A series of hierarchical porous carbons (HPCs) with different morphologies and well-developed porosity have been successfully synthesized via a facile and flexible template-free method using hierarchical assembly of polyimide as carbon precursor. Amongst, cornflower-like hierarchical porous carbon (FC4) displays the best CO2 capture property with an adsorption capacity up to 4.05 and 2.87 mmol g−1 at 273 and 298 K, respectively. The excellent CO2 capture capability of FC4 can be owing to the cooperative effect of moderate meso-/macropore channels and abundant framework micropores, which are conducive to diffusion and capture of CO2 adsorbate. Moreover, FC4 shows superior stability and recyclability and CO2 trapping selectivity with CO2/N2 initial and final adsorption ratios of 24 and 6.4, respectively. It can be anticipated that the FC4 is a promising adsorbent in the adsorption and separation of carbon dioxide under actual conditions.

Gadolinium (Gd) has been used as a dopant to modify MnOx for enhanced catalytic performance and sulfur resistance in the application of the selective catalytic reduction (SCR) of NOx with NH3 for the first time. The results show that the introduction of Gd with proper amount can effectively restrain the crystallization of MnOx, enhance the specific surface area, increase the concentrations of surface Mn4+ and chemisorbed oxygen species, and enhance the amount and the strength of surface acid sites. The MnGdO-2 catalyst (Gd-modified MnOx with the mole ratio of Gd/Mn = 0.1) exhibits optimal catalytic performance among all prepared catalysts with a 100% NO conversion performance in a wide temperature window from 120 to 330 °C and a 100% N2 selectivity from 150 to 300 °C under a high space velocity of 36,000 h−1. In-situ DRIFT spectra reveal that the Gd doping can promote the NH3 adsorption on the catalyst pre-adsorbed with NOx species, facilitating the reactive NH4+ species taking part in the SCR reaction. More importantly, MnGdO-2 catalyst presents stronger resistance to water vapor or sulfur poisoning in comparison with pure MnOx catalyst, which can be ascribed to these facts that Gd-modification restrains the transformation of MnO2 to Mn2O3 and the generation of MnSO4, impedes the decrease in Lewis acid sites and the increase in Bronsted acid sites, and alleviates the competitive adsorption between the NO and SO2. This work may provide new insights into the effects of rare earth modification on the de-NOx mechanism and the SO2 resistance mechanism of MnOx catalysts.

A new photocatalyst, the tri-arm CdS/ZnS core–shell nanorod, is carefully designed for the first time, where tri-arm CdS nanorods are decorated by dodecylamine (DDA) molecules and then wrapped in an intermittent ZnS shell. The resultant photocatalyst with a CdS/ZnS mole ratio of 0.5 (CZS0.5) presents a significantly improved H2 evolution rate of 726.0 μmol/h (3 mg of catalysts, equal to 242.0 mmol/g/h) in the absence of co-catalysts, which is currently the highest value in CdS-based catalysts. The apparent quantum efficiency of CZS0.5 reaches 50.61% at 380 nm. The significantly enhanced photocatalytic performance can be attributed to a win–win situation between the analogous type-II mechanism formed in the CdS/ZnS heterojunction and the H+ adsorption resulting from the DDA molecules. Due to the analogous type-II mechanism, photogenerated electrons are transferred from the ZnS shell to the CdS nanorod. Owing to the decoration of DDA, many H+ ions are adsorbed on CdS. Thus, the photogenerated electrons gathered in CdS can be captured quickly and in a timely manner by the adsorbed proton H+ to produce hydrogen, which effectively suppresses the recombination of photogenerated electrons and holes. This study may bring new insights for developing other photocatalysts with high performance by using small organic molecules.

The stability of MnO x based low temperature SCR catalysts remained to be a serious issue. This report explored use of multi-walled carbon nanotubes (MWCNTs) network with uniform structure as a “rigid” pore template for synthesis of mesoporous MnO x -TiO 2 SCR catalyst with high surface area and high stability. The results showed that MWCNT network imposed MnO x -TiO 2 catalyst a mesoporous porosity with a narrow pore size distribution centered on ∼13.2 nm and a surface area of 131.6 m 2 g −1 stabilized at 500 °C. The mesoporous structure was formed by interconnected nanoparticles, comprised of crystallized rutile TiO 2 core surrounded by amorphous MnOx, with an average diameter of ∼8 nm. The catalyst exhibited an excellent low temperature SCR activity and selectivity as well as high resistance to deactivation and poison by H 2 O and SO 2 . SnO 2 modification led to degradation of catalytic performance in low temperature (60–180 °C) side, but improvement at high temperature side (240–360 °C), especially at high gas velocity, which can be attributed to change in structure, reactivity of MnO x and surface acidity induced by SnO 2 addition.

MnM2O4 microspheres (M = Co, Cu, Ni) were successfully prepared by a hydrothermal method. The catalytic activities of the as-prepared MnM2O4 microspheres were comparatively investigated by the selective catalytic reduction (SCR) of NO with NH3, and their reaction mechanisms were studied by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). The results showed that MnCo2O4 presented the best low-temperature catalytic activity (nearly 100% NOx conversion in a wide temperature window from 120 to 330 °C under a high gas hourly space velocity (GHSV) of 36,000 h−1), the best N2 selectivity (100% N2 selectivity in the temperature range from 60 to 360 °C), and excellent water resistance. The high catalytic activity of MnCo2O4 was mainly attributed to the large quantity of surface acid sites with dominant Bronsted acid sites rather than Lewis acid sites. In addition, larger SBET and higher surface Mn4+ concentration also had positive effect on its catalytic activity. Contrastively, the least number of surface acid sites with dominant Lewis acid sites rather than Bronsted acid sites over MnCu2O4 resulted in its worst low-temperature catalytic activity. The catalytic activity of MnNi2O4 was in the middle. In-situ DRIFT revealed that the NH3-SCR of NO over MnCo2O4 and MnNi2O4 followed both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. For MnCu2O4, the reaction was dominated by E-R mechanism.

Developing photocatalysts with high charge separation and transfer efficiency remains a key challenge for photocatalytic water-splitting reaction. In this work, a facial approach was explored to successfully realize the in situ growth of g-C3N4 on the surface of C-doped TiO2 hollow nanospheres (C-TiO2). The as-obtained heterogeneous photocatalyst, C-TiO2@g-C3N4 (TCN), presented core-shell hollow nanosphere structure. Systematic studies disclose that the TCN photocatalysts exhibit remarkably enhanced visible-light photocatalytic activity for water splitting to produce H2 compared with the pristine C-TiO2 and g-C3N4. The TCN-2 photocatalyst (the weight ratio of initial urea and C-TiO2 is 2:1) presents the highest H2 generation rate of 35.6 μmol g−1 h−1, which is 22.7 and 10.5 times higher than that of C-TiO2 and g-C3N4, respectively. The enhanced photocatalytic performance can be attributed to the formation of the heterojunction between the two semiconductors, which effectively promotes the separation of photo-generated carriers. Meanwhile, the intimate contact between the C-TiO2 and g-C3N4 resulted from the in situ growth greatly improves the separation and transfer efficiency of photo-generated carries. Besides, the enhancement in the utilization efficiency of light energy due to the unique hollow structure also exhibits a positive contribution.

Herein, a new photocatalyst (UiOS-Cu-CdS/ZnS, abbreviated as SCu-CZS) with hierarchical structure is well-designed by loading CdS/ZnS quantum dots (QDs) onto Cu (II) decorated thiol-functionalized UiO-66 (UiOS-Cu) metal-organic frameworks (MOFs) for water splitting, where CdS and ZnS QDs are evenly distributed on the surface and in the channels of MOF, respectively, and Cu (II) ions are connected with thiol groups. We find that the UiOS-Cu, as an efficient medium for the separation and transfer of charge carriers between CdS and ZnS, successfully transforms the I-type transfer mechanism of charge carriers in CdS/ZnS heterojunction into II-type transfer mechanism, in which the decoration of Cu (II) plays a key role. Due to the decoration of Cu (II), the highest occupied molecular orbital (HOMO) of UiOS-Cu is markedly lifted to the position higher than the valence band (VB) of CdS, promoting the smooth transfer of photoinduced holes from the VB of CdS to the HOMO of UiOS-Cu. Thanks to this II-type transfer mechanism, the photogenerated electrons and holes are effectively separated and transferred, significantly improving the photocatalytic H2 evolution performance. The optimized SCu-CZS sample exhibits a high H2 generation rate of 425.5 μmol/h (10 mg of catalyst) with an apparent quantum efficiency of 24.6% at the wavelength of 365 nm in the absence of noble metal co-catalyst. This work indicates that MOF can be used as an efficient transfer medium of charge carriers, promoting photocatalytic hydrogen evolution by transforming the transfer mechanism of photogenerated electrons and holes, which provides a new idea for the construction of MOF-based photocatalysts.

The interface defects caused by lattice mismatch between semiconductors and the homogeneous doping of dopants in host semiconductors without layered structure are the challenges in the construction of high performance photocatalysts. Herein, a smart template induced in-situ growth method is developed to synthesize a quantum dot level Cu&In co-doped CdS (CuIn-CdS) hetero-phase junction with multi-arm nanorod morphology for the first time. Due to the in-situ growth of CdS induced by Cu-doped In2S3 nanorods, the homogeneous doping of Cu and In in CdS is easily realized, which efficiently expands the light absorption ability of CdS. Moreover, owing to the hetero-phase junction formed between hexagonal and cubic CdS rather than heterostructure, the lattice mismatch and the interface defects are greatly minimized, which effectively facilitates the separation and transfer of photogenerated charge carriers. As a result, the optimal CuIn-CdS exhibits a photocatalytic H2 evolution rate of 105.44 mmol/g/h (corresponding to the apparent quantum efficiency (AQE) of 32.72% at 400 nm), which is about 55.0, 10.9 and 9.7 times higher than that of pristine CdS, Cu-CdS and In-CdS, respectively. This work provides a new way to overcome interface defects and realize homogeneous doping at the same time for exploring new photocatalysts with high performance.

This research aims to enhance the SO2 tolerance of manganese oxide (MnOx) catalysts for low-temperature selective catalytic reduction (SCR) de-NOx. Based on the deactivation mechanism of MnOx, we target at the promotion of the byproduct (NH4HSO4) decomposition and the inhibition of the byproduct (MnSO4) formation. To achieve this target, thermogravimetric (TG) and temperature programmed desorption of SO2 (SO2-TPD) are performed upon as many as 21 kinds of single metal oxides to explore the potentially effective chemical composition as the additive of MnOx catalysts. The TG result indicates that Al2O3 can remarkably decrease the thermal stability of NH4HSO4. In addition, the SO2-TPD analysis reveals that the formed species after SO2 adsorption are weakly adsorbed on Al2O3. Thus, Al2O3 is selected to mix with MnOx to optimize its SO2 tolerance. Further experimental results demonstrate that the proper introduction of Al2O3 can effectively enhance the low-temperature SCR de-NOx activity and the SO2 tolerance of MnOx. It is revealed that the introduction of Al2O3 into MnOx can not only facilitate the decomposition of NH4HSO4 but also lead to reduced thermal stability of the adsorbed SO2 species to some extent. As compared to the pristine MnOx, the slight introduction of Al2O3 as the additive is beneficial to the low-temperature SCR de-NOx activity and SO2 tolerance of MnOx.

As a sustainable technology, semiconductor photocatalysis has attracted considerable interest in the past decades owing to its potential to relieve energy and environmental issues. By virtue of their unique structural and electronic properties, emerging ultrathin 2D materials show enormous potential to achieve efficient photocatalytic performance. Herein, we report the fabrication of 2D/2D ZnxCd1−xIn2S4/g-C3N4 heterostructure via a facile hydrothermal method for visible-light-driven photocatalytic H2 evolution. By tailoring the energy band structure of the ZnxCd1−xIn2S4 solid solutions, the position of conduction band can be largely elevated and thus achieve a strong photoreduction capability. A further construction of 2D/2D ZnxCd1−xIn2S4/g-C3N4 heterojunction can reduce charge transfer distance from inner part to surface and create abundant interfacial charge transfer pathways, resulting in significantly boosted migration and separation efficiency of photogenerated charge carriers. Consequently, this energy band engineering effect combined with the advantages of the unique 2D/2D architecture endows the ZnxCd1−xIn2S4/g-C3N4 heterojunction with a remarkable H2 evolution rate of 170.3 μmol h−1 under visible-light irradiation (λ > 420 nm) in the absence of co-catalyst, which is nearly 4.5 and 567.7 times that of Zn1/2Cd1/2In2S4 (37.8 μmol h−1) and pure g-C3N4 (0.3 μmol h−1), respectively. Furthermore, the apparent quantum yield (AQY) and the solar-to-hydrogen (STH) energy conversion efficiency over Zn1/2Cd1/2In2S4/CN are 8.5% and 2.6%, respectively. This study sheds light on the potential of integrating the two strategies of energy band modulation and 2D/2D heterojunction into designing semiconductor photocatalysts for highly efficient solar-to-energy conversion applications.

Photocatalysis is a promising method to obtain hydrogen without any pollution. The key to improve the efficiency of photocatalytic reaction is to design an excellent catalyst structure which can effectively promote the separation and transfer of photogenerated electrons and holes. In this work, a novel photocatalyst, Ni2P decorated NiO/g-C3N4 p-n junction (NiO/Ni2P/CN, abbreviating g-C3N4 as CN) is successfully developed by a one-step in-situ phosphating of Ni(OH)2/CN. The optimized NiO/Ni2P/CN exhibits an impressive photocatalytic H2 evolution rate of 5.04 μmol h−1 under visible-light irradiation (λ > 420 nm) without any noble metal as co-catalyst, which is 126 times higher than that of pristine CN. This high photocatalytic performance is mainly based on the intimated contact of the three components (Ni2P, NiO and CN), where the photogenerated holes on the valence band (VB) of CN can be transferred to the VB of NiO due to the internal-built electric field created by p-n junction, while the photoexcited electrons on the conduction band (CB) of CN can be migrated to Ni2P co-catalyst with a low overpotential, thus the separation and transfer of charge carriers are significantly promoted, and finally the photocatalytic activity of NiO/Ni2P/CN for the hydrogen evolution from water splitting is enhanced. This work may enlighten on the design of photocatalysts with high efficiency by constructing p-n junction and metal phosphide co-catalyst with low overpotential.

Zn 2 GeO 4 nanobelts modified by CdS quantum dots (Zn 2 GeO 4 /CdS) were prepared successfully by chemical bath deposition. The novel photocatalyst was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and UV–Vis diffuse reflectance spectroscopy. It was found that Zn 2 GeO 4 /CdS consisted of uniform rhombohedral phase Zn 2 GeO 4 nanobelts with highly dispersed cubic phase CdS quantum dots, and the Zn 2 GeO 4 /CdS exhibited strong visible light absorption at about 510 nm. The photocatalytic activities of the catalysts were evaluated by the discoloration of Rhodamine B under visible light illumination and were compared with that of pure Zn 2 GeO 4 nanobelts. The results suggested that the composite photocatalyst had much higher photocatalytic activities than pure Zn 2 GeO 4 nanobelts under irradiation of visible light. Meanwhile, no obvious deactivation of Zn 2 GeO 4 /CdS was observed after the three recycles experiments in photodegradation of RhB. The possible mechanism of visible light photocatalytic degradation is also proposed.

Carbon-doped titania hollow spheres (THS) with unique hollow three-dimensional network structure were synthesized by a facile method using carbon spheres as template. The resultant samples, such as carbon spheres, carbon spheres coated with titania precursor, and final THS were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FTIR), Brunauer–Emmett–Teller (BET) and UV–vis absorption spectrum. Based on the results of these characterizations, a reasonable formation mechanism of the hollow three-dimensional network structure was proposed. The photocatalytic activity of as-prepared THS was evaluated by decoloration of methylene blue solution under visible light irradiation. Results indicated that THS possessed higher visible light-induced photocatalytic activity than commercial P25, which could be attributed to its visible light absorption characteristic created by C-doping and the unique hollow three-dimensional network structure.