Showing papers in "Applied Catalysis B-environmental in 2015"

Sulfur-doped g-C3N4 with enhanced photocatalytic CO2-reduction performance

Abstract: Graphitic carbon nitride (g-C 3 N 4 ) is the most stable phase of all carbon nitride allotropes under ambient conditions. In this study, sulfur-doped g-C 3 N 4 was fabricated by simply calcinating thiourea at 520 °C. Sulfur-doped g-C 3 N 4 (TCN) was found to absorb light up to 475 nm corresponding to a band gap of 2.63 eV, which was narrower than that of un-doped g-C 3 N 4 (MCN) with a band gap of 2.7 eV. First-principle calculations based on spin-polarized density functional theory were utilized to investigate the theoretical partial density of states of the TCN and MCN, indicating that the band gaps of TCN and MCN were the same, but impurities existed in the TCN sample. Consequently, photogenerated electrons could easily jump from the impurity state to the conduction band or from the valence band to the impurity state. Photocatalytic CO 2 reduction was further used to evaluate the photoactivity of samples, and the CH 3 OH yield using TCN and MCN were 1.12 and 0.81 μmol g −1 , respectively. PL spectrum analysis and transient photocurrent responses were also carried out to verify the suggested photocatalysis mechanism.

Sulfate radicals induced from peroxymonosulfate by magnetic ferrospinel MFe2O4 (M = Co, Cu, Mn, and Zn) as heterogeneous catalysts in the water

Abstract: Magnetic ferrospinel MFe 2 O 4 (M = Co, Cu, Mn, and Zn) prepared in a sol–gel process was introduced as catalyst to generate powerful radicals from peroxymonosulfate (PMS) for refractory di-n-butyl phthalate (DBP) degradation in the water. Various catalysts were described and characterized, and the catalytic activities in PMS oxidation system were investigated. Most important of all, the mechanism of different catalysts in the catalytic PMS solution was illustrated. The results showed that the incorporation of CoFe 2 O 4 had the highest catalytic performance in PMS oxidation for DBP degradation. All catalysts presented favorable recycling and stability in the repeated batch experiment. The catalytic process showed a dependence on initial pH, and an uncharged surface of the catalyst was more profitable for sulfate radical generation. H 2 -TPR and CVs analysis indicated that the sequence of the catalyst's reducibility in PMS solution was CoFe 2 O 4 > CuFe 2 O 4 > MnFe 2 O 4 > ZnFe 2 O 4 , which had a close connection with the activity of metal ion in A site of the catalysts. The surface hydroxyl sites played an important role in the catalytic process, and its quantity determined the degradation of DBP. Moreover, the reactive species in PMS/MFe 2 O 4 system were identified as sulfate radical and hydroxyl radical. The promotion of these radical's reaction was due to the fact that a balance action in the process of M 2+ /M 3+ , O 2− /O 2 , occurred, and at the same time, PMS was catalyzed.

Self-Cleaning Applications of TiO2 by Photo-Induced Hydrophilicity and Photocatalysis

Abstract: Self-cleaning materials have gained considerable attention for both their unique properties and practical applications in energy and environmental areas. Recent examples of many TiO2-derived materials have been illustrated to understand the fundamental principles of self-cleaning hydrophilic and hydrophobic surfaces. Various models including those proposed by Wenzel, Cassie-Baxter and Miwa-Hashimoto are discussed to explain the mechanism of self-cleaning. Examples of semiconductor surfaces exhibiting the simultaneous occurrence of superhydrophilic and superhydrophobic domains on the same surface are illustrated, which can have various advanced applications in microfluidics, printing, photovoltaic, biomedical devices, anti-bacterial surfaces and water purification. Several strategies to improve the efficiency of photocatalytic self-cleaning property have been discussed including doping with metals and non-metals, formation of hetero-junctions between TiO2 and other low bandgap semiconductors, and fabrication of graphene based semiconductor nano-composites. Different mechanisms such as band-gap narrowing, formation of localized energy levels within the bandgap and formation of intrinsic defects such as oxygen vacancies have been suggested to account for the improved activity of doped TiO2 photocatalysts. Various preparation routes for developing efficient superhydrophilic–superhydrophobic patterns have been reviewed. In addition, reversible photo-controlled surfaces with tuneable hydrophilic/hydrophobic properties and its technological applications are discussed. Examples of antireflective surfaces exhibiting self-cleaning properties for the applications in solar cells and flat panel displays have also been provided. Discussion is provided on TiO2 based self-cleaning materials exhibiting hydrophilic and underwater superoleophobic properties and their utilities in water management, antifouling applications and separation of oil in water emulsions are discussed. In addition, ISO testing methods (ISO 27448: 2009, ISO 10678: 2010 and ISO 27447: 2009) for analysing self-cleaning activity and antibacterial action have also been discussed. Rapid photocatalytic self-cleaning testing methods using various photocatalytic activity indicator inks such as resazurin (Rz), basic blue 66 (BB66) and acid violet 7(AV7) for a broad range of materials such as commercial paints, tiles and glasses are also described. Various commercial products such as glass, tiles, fabrics, cement and paint materials developed based on the principle of photo-induced hydrophilic conversion of TiO2 surfaces have also been provided. The wide ranges of practical applications of self-cleaning photocatalytic materials suggest further development to improve their efficiency and utilities. It was concluded that a rational fabrication of multifunctional photocatalytic materials by integrating biological inspired structures with tunable wettability would be favorable to address a number of existing environmental concerns.

Ultrathin hexagonal SnS2 nanosheets coupled with g-C3N4 nanosheets as 2D/2D heterojunction photocatalysts toward high photocatalytic activity

Abstract: In this work, we present the 2D/2D type of heterojunction photocatalysts fabricated by horizontal loading ultrathin hexagonal SnS2 nanosheets on g-C3N4 nanosheets through a facile ultrasonic dispersion method. The sheet-like structures of these two nanomaterials induce a large contact region in the heterojunction interface, as evidenced by electron microscopic analyses. By taking advantage of this feature, the as-fabricated SnS2/g-C3N4 heterojunction nanosheets exhibit considerable improvement on the photocatalytic activities for the degradation of organic dyes and phenols under visible light irradiation as compared to pure g-C3N4 and SnS2 nanosheets. In particular, the optimal heterojunction nanosheet with 5.0 wt.% SnS2 shows the apparent rate constant of ∼0.2 min−1 for the RhB photodegradation, which is higher than that of pure g-C3N4 and SnS2 nanosheets by a factor of 4 and 8, respectively. Further studies by steady-state and transient photoluminescence spectroscopy indicate that the photosynergistic effect of SnS2/g-C3N4 heterojunction can remarkably enhance the photoinduced interfacial charge transfer, thereby increasing the charge separation during the photocatalytic reaction.

Preparation of magnetite-based catalysts and their application in heterogeneous Fenton oxidation – A review

Abstract: This study presents a critical review on the application of magnetite-based catalysts to industrial wastewater decontamination by heterogeneous Fenton oxidation. The use of magnetic materials in this field started only around 2008 and continues growing increasingly year by year. The potential of these materials derives from their higher ability for degradation of recalcitrant pollutants compared to the conventional iron-supported catalysts due to the presence of both Fe(II) and Fe(III) species. In addition, their magnetic properties allow their easy, fast and inexpensive separation from the reaction medium. The magnetic materials applied up to now can be classified in three general groups: magnetic natural minerals, in-situ-produced magnetic materials and ferromagnetic nanoparticles. A survey of the catalysts investigated so far is presented paying attention to their nature and competitive features in terms of activity and durability.

Synthesis and applications of novel graphitic carbon nitride/metal-organic frameworks mesoporous photocatalyst for dyes removal

Abstract: Metal-organic frameworks (MOFs) have been attracted considerable attention for their applications in gas storage/separation, adsorption as well as catalysis. In this study, a facile solvothermal method was employed to prepare MOFs and graphitic carbon nitride (g-C3N4) hybrids, and a g-C3N4/Ti-benzenedicarboxylate (MIL-125(Ti)) heterostructures photocatalyst was successfully synthesized. The as-obtained materials were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption–desorption isotherm, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflection spectroscopy (UV–vis DRS), and photoluminescence (PL) spectroscopy. It is indicated that the hybrids have large surface area, mesoporous structure, thermal stability, and enhanced visible-light absorption. Compared with pure MIL-125(Ti) and g-C3N4, the composites exhibited more efficient photocatalytic performance for Rhodamine B degradation from aqueous solution under visible-light irradiation. The optimal g-C3N4 content in g-C3N4/MIL-125(Ti) composite was determined to be 7.0 wt%, and the corresponding photodegradation rate for RhB was 0.0624 min−1, about 2.1 and 24 times higher than that of pure g-C3N4 and MIL-125(Ti), respectively. The indirect dye photosensitization, the Ti3+–Ti4+ intervalence electron transfer, and the synergistic effect between MIL-125(Ti) and g-C3N4 were the three reasons for improved photo-degradation performance. Therefore, it is reasonable to believe that metal-free semiconductor/MOFs photocatalysts have great potentiality in environmental remediation.

Solar photocatalysis: Materials, reactors, some commercial, and pre-industrialized applications. A comprehensive approach

Abstract: In the future, solar energy, along with other renewable resources, could play a key role in mass production of fine chemicals. It could also potentially solve environmental problems, as demonstrated by recent developments in the use of solar energy, such as solar photocatalysis. The solar photocatalytic technology has been demonstrated to be effective for: • Treating groundwater, drinking water, industrial wastewater, and air and soil pollution, • Water disinfection, and • Industrial production of fine chemicals. This report summarizes the current status of solar photocatalysis and identifies future opportunities for research and industry in this field, including recent relevant bibliography. The main commercial solar photocatalytic applications are described, included the technologies based on sunlight for antifogging and self-cleaning of coating materials, glass, and concrete. An overview of several different solar photoreactors and the main operating process parameters are also provided. For the estimation of capital costs, it is suggested the use of appropriate “figures of merit”. The present review would be of interest for researchers, technologists, engineers, and industrialists.

Novel visible-light-driven CQDs/Bi2WO6 hybrid materials with enhanced photocatalytic activity toward organic pollutants degradation and mechanism insight

Abstract: Novel visible-light-driven carbon quantum dots (CQDs)/Bi2WO6 hybrid materials were synthesized via a facile hydrothermal method. Multiple techniques were applied to investigate the structures, morphologies, optical and electronic properties and photocatalytic performance of as-prepared samples. The nanostructured hybrid material was formed with CQDs attached on the surface of Bi2WO6 sphere-like structure. The photocatalytic activity of the CQDs/Bi2WO6 hybrid materials was evaluated sufficiently by using rhodamine B (RhB), colorless antibiotic agent ciprofloxacin (CIP), tetracycline hydrochloride (TC), and endocrine disrupting chemical bisphenol A (BPA), as target organic pollutants. The as-prepared CQDs/Bi2WO6 hybrid materials exhibited much higher photocatalytic activities than pure Bi2WO6, which showed a broad spectrum of photocatalytic degradation activity. The enhanced activities were attributed to the interfacial transfer of photogenerated electrons from Bi2WO6 to CQDs, leading to effective charge separation of Bi2WO6. The modification by using CQDs (electron acceptor) was an effective way to improve photocatalytic efficiency, which can be extended to a general strategy for other semiconductors. The ESR analysis and free radicals trapping experiments indicated that the O2 − and h+ were the main active species for the photocatalytic degradation. A possible mechanism of CQDs for the enhancement of visible light performance was proposed.

Enhanced photocatalytic activity and stability of Z-scheme Ag2CrO4-GO composite photocatalysts for organic pollutant degradation

Abstract: Silver chromate-graphene oxide (Ag2CrO4-GO) composites are prepared by a facile precipitation method. The resulting Ag2CrO4-GO composites exhibit excellent photocatalytic activity and stability towards the degradation of the dyes and phenol in aqueous solution under visible-light irradiation. The optimal composite with 1.0 wt% GO content shows the highest photocatalytic activity for methylene blue (MB) degradation, which is 3.5 times that of pure Ag2CrO4 particles. The enhanced photocatalytic activity is mainly attributed to the formation of Ag2CrO4-GO Z-scheme heterojunction that can not only facilitate the separation and transfer of the photogenerated charge carriers, but also preserve a strong oxidation and reduction ability. The high photocatalytic stability is due to the successful inhibition of the photocorrosion of Ag2CrO4 by transferring the photogenerated electrons of Ag2CrO4 to GO. The present work provides a new understanding into design and fabrication of the GO/silver compound composite photocatalysts.

Efficient synthesis of monolayer carbon nitride 2D nanosheet with tunable concentration and enhanced visible-light photocatalytic activities

Abstract: A versatile and scalable mixed solvent strategy was developed to prepare monolayer C3N4 nanosheets with tunable concentration for the first time. This approach could also be used to prepare other 2D nanosheets from their layered materials (such as MoS2, BN, WS2 etc.). The structural features and intrinsic semiconductor properties of the as-prepared C3N4 nanosheets have been investigated in detailed. The photocatalytic activities were evaluated by photocatalytic oxidation of both benzyl alcohol and rhodamine B (RhB) under visible light irradiation. Results showed that the as-prepared monolayer C3N4 nanosheets with thickness of 0.4 nm still retained the structural features of g-C3N4 layer. The functionalities of C3N4 nanosheets well inherited from the layered parent counterpart. Furthermore, due to the exceptionally high 2D anisotropy, C3N4 nanosheets showed the distinctive physicochemical properties and unique electronic structures, such as high surface area, lower surface defects, stronger reduction ability of the photogenerated electrons, increased photoelectric response, and promoted the charge-carrier migration and separation. All of these favorable factors co-contributed to the greatly improved photocatalytic activities over C3N4 nanosheets compared with those of its bulk counterpart.

Effect of contact interface between TiO2 and g-C3N4 on the photoreactivity of g-C3N4/TiO2 photocatalyst: (001) vs (101) facets of TiO2

Abstract: In this paper, effect of contact interfaces of high-energy TiO 2 , (1 0 1) and (0 0 1) facets, with g-C 3 N 4 on the photocatalytic activity of g-C 3 N 4 /TiO 2 hybrid was studied using TiO 2 hollow nanobox (TiO 2 -HNB) assembly from high-energy TiO 2 nanosheets (TiO 2 -NS) as model. The prepared photocatalyst was characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM), nitrogen sorption, Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectrometer (XPS). The photoreactivity of the photocatalyst was evaluated by measure the formation rate of photo-induced hydroxyl radicals ( OH) using coumarin as a probe molecule and photocatalytic degradation of Brilliant Red X3B (an anionic dye) under UV irradiation ( λ = 365 ± 10 nm). It was found that g-C 3 N 4 /TiO 2 -HNB forms direct Z-scheme photocatalytic system, which shows superior enhancement on the photocatalytic activity of TiO 2 than g-C 3 N 4 /TiO 2 -NS. It is by contacting g-C 3 N 4 with (1 0 1) facets, g-C 3 N 4 can efficient remove the photo-generated electrons accumulated on (1 0 1) facets of high-energy TiO 2 , which results in spatially isolated photo-generated electrons and holes, enhancing the photocatalytic activity.

Vertical single or few-layer MoS2 nanosheets rooting into TiO2 nanofibers for highly efficient photocatalytic hydrogen evolution

Abstract: The catalytic activity of molybdenum sulfide (MoS 2 ) for hydrogen evolution reaction (HER) strongly depends on the number of exposed active edges of MoS 2 nanosheets. Making single or few-layer MoS 2 nanosheets vertically stand on a substrate is a very effective way to maximally expose the edge sites of MoS 2 nanosheets. Vertically standing single or few-layer MoS 2 nanosheets on porous TiO 2 nanofibers (TiO 2 @MoS 2 ) are successfully prepared via a simple hydrothermal reaction. Due to plenty of pores in the electrospun TiO 2 nanofibers, the MoS 2 nanosheets vertically grow from the inside to the outside, and the growth mode of the MoS 2 nanosheets rooting into the TiO 2 nanofibers endows not only intimate contact between TiO 2 and MoS 2 for fast electrons transfer but also high structural stability of TiO 2 @MoS 2 heterostructure. The vertical orientation of MoS 2 nanosheets enables the active edge sites of MoS 2 to be maximally exposed. Without using Pt cocatalyst, the TiO 2 @MoS 2 heterostructure achieves high photocatalytic hydrogen production rates of 1.68 or 0.49 mmol h −1 g −1 under UV–vis or visible light illumination, respectively. This high photocatalytic activity arises from the positive synergetic effect between the MoS 2 and TiO 2 components in this novel heterostructure. In addition, the TiO 2 @MoS 2 heterostructure exhibits a high durability as evidenced by the invariable hydrogen production rate after continuous illumination over 30 h. The work advances the development of highly efficient molybdenum sulfide-based HER catalysts.

High-efficiency conversion of CO2 to fuel over ZnO/g-C3N4 photocatalyst

Abstract: The objective of this research was to prepare, characterize and evaluate the conversion efficiency of CO2 to fuel on a ZnO/g-C3N4 composite photocatalyst under simulated sunlight irradiation. The photocatalyst was synthesized by a simple impregnation method and was characterized by various techniques, including Brunauer–Emmett–Teller method (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence spectroscopy (PL). The characterizations indicate that ZnO and g-C3N4 were uniformly combined. The deposition of ZnO on g-C3N4 showed nearly no effect on its light-absorption performance. However, the interactions between the two components promoted the formation of a hetero-junction structure in the composite, inhibited the recombination of electron–hole pairs and, finally, enhanced the photocatalytic performance of ZnO/g-C3N4. The optimal ZnO/g-C3N4 photocatalyst showed a CO2 conversion rate of 45.6 μmol h−1 gcat−1, which was 4.9 and 6.4 times higher than those of g-C3N4 and P25, respectively. This work represents an important step toward artificial photocatalytic CO2 conversion to fuel using cost-efficient materials.

Mesoporous manganese oxides prepared by solution combustion synthesis as catalysts for the total oxidation of VOCs

Abstract: Three mesoporous manganese oxide catalysts (Mn 2 O 3 , Mn 3 O 4 and Mn x O y ) have been prepared, by means of the solution combustion synthesis, and tested for the total oxidation of volatile organic compounds (VOCs; ethylene, propylene, toluene and their mixture). The best results, in terms of the total oxidation of VOCs, were achieved with the Mn 3 O 4 catalyst, which showed the highest amount of electrophilic oxygen on the surface (O α -species). The most active powder catalyst was then deposited on a cordierite-type monolith through a novel direct synthesis and tested for the total oxidation of the VOCs mixture. The Mn 3 O 4 -based monolith exhibited high activity towards the total oxidation of VOCs, which is comparable to that obtained with powdered Mn 3 O 4 . The monolithic catalyst showed excellent catalytic activity for the total combustion of the mixture of VOCs (conversion to CO 2 = 99.2% ± 0.5) over a time-on-stream of 10 h at 310 °C and no deactivation occurred during this time span.

Ni@Pd core–shell nanoparticles modified fibrous silica nanospheres as highly efficient and recoverable catalyst for reduction of 4-nitrophenol and hydrodechlorination of 4-chlorophenol

Abstract: In this study, a novel fibrous nano-silica (KCC-1) based nanocatalyst (Ni@Pd/KCC-1) was synthesized by modifying KCC-1 using Ni@Pd core–shell nanoparticles (NPs). The Ni@Pd/KCC-1 was used in the catalytic reduction of 4-nitrophenol (4-NP) and hydrodechlorination (HDC) of 4-chlorophenol (4-CP). KCC-1, prepared by hydrothermal method, exhibited a dandelion-like shape, high surface area, and easy accessibility of active sites. The Ni@Pd NPs possessed a magnetic nickel (Ni) core with palladium (Pd) shell structural composite. Thus, use of Ni led to the reduced consumption of Pd without sacrificing the overall catalytic performance, simultaneously making it reusable as it could be conveniently recovered from the reaction mixture by using an external magnetic field. Immobilization of the Ni@Pd NPs on KCC-1 nanospheres not only prevented their aggregation, but also significantly enhanced the accessibility of the catalytic active sites. The Ni@Pd/KCC-1 nanocatalyst displayed excellent catalytic activities for both the reduction of 4-NP and the HDC of 4-CP under green conditions. The above-mentioned approach based on fibrous KCC-1 and Ni@Pd NPs provided a useful platform for the fabrication of noble metal-based cost-effective nanocatalyst with easy accessibility, and acted as a promising candidate for numerous catalytic applications.

Photocatalytic CO2 reduction by CdS promoted with a zeolitic imidazolate framework

Abstract: Metal organic frameworks (MOFs) have emerged as a new class of multifunctional porous materials, and more particularly the family of zeolitic imidazolate frameworks (ZIFs) have shown great promise in the applications of carbon dioxide capture and storage. The CO 2 photoreduction system was established by employing CdS semiconductor and Co-ZIF-9 to act as a catalyst and a cocatalyst, respectively. This hybrid system cooperating with bipyridine and triethanolamine exhibits high catalytic activity in the deoxygenative conversion of CO 2 to CO under visible light irradiation at mild reaction conditions. 13 CO 2 isotopic experiment validated that the produced CO was from the photoreduction of CO 2 , instead of organics in the system. The effect of parameters such as cocatalyst concentration, reaction temperature, solvent properties, and water effect were investigated in details. Under the optimized reaction conditions, a high apparent quantum yield of 1.93% was achieved under monochromatic irradiation of 420 nm. The uniqueness of Co-ZIF-9 in supporting CdS for CO 2 reduction reaction was explored by comparing its catalytic functions with other MOFs. In-situ photoluminescence and photocurrent generation measurements demonstrated the function of Co-ZIF-9 for promoting electron transfers. At last, a possible reaction mechanism of the photoreduction reaction was proposed.

Catalytic reactions of gamma-valerolactone: A platform to fuels and value-added chemicals

Abstract: Gamma-valerolactone (GVL), which is accessible from renewable lignocellulosic biomass, has been identified as one of the most promising platforms for the sustainable production of fuels and value-added chemicals. This review aims at recent advances in the catalytic production of GVL from biomass and further upgrading of GVL to fuels as well as value-added chemicals. The first part briefly reviews recent advances for the production of GVL from biomass. The second and third sections critically review and identify current technologies for the efficient production of GVL. The mechanism, different types of advanced homogeneous and heterogeneous catalysts employed have been compared and broadly categorized. Challenges and areas that need improvement are also highlighted in the corresponding area. The fourth section concentrates on potential applications and the upgrading of GVL to fuel additives, diesel fuels and value-added chemicals. The final section offers a summary and future perspective in the field.

3D-hierarchically structured MnO2 for catalytic oxidation of phenol solutions by activation of peroxymonosulfate: Structure dependence and mechanism

Abstract: Hierarchical materials have facilitated fascinating applications in heterogeneous catalysis due to that micro-sized bulk is easily separable and nano-sized sub-blocks can significantly enhance catalytic performance. In this study, corolla-like δ-MnO2 with sub-blocks of nanosheets, and urchin-shaped α-MnO2 with sub-blocks of nanorods were synthesized by a simple hydrothermal route. The hydrothermal temperature significantly influenced the crystal structure, morphology and textural structure of the obtained three-dimensional (3D) MnO2 catalysts. The catalytic activities of three samples prepared at 60, 100 and 110 °C (denoted as Mn-60, -100 and -110, respectively) were thoroughly evaluated by activation of peroxymonosulfate (PMS) for catalytic oxidation of phenol solutions. Based on first-order kinetics, the rate constants of Mn-60, -100 and -110 catalysts were determined to be 0.062, 0.132, and 0.075 min−1, respectively. The activation energy of Mn-100 in catalytic oxidation of phenol solutions was estimated to be 25.3 kJ/mol. The catalytic stability of Mn-100 was also tested and discussed by monitoring Mn leaching. Electron paramagnetic resonance (EPR), quenching tests, total organic carbon (TOC) analysis and identification of intermediates were applied to illustrate the activation processes of PMS and the mechanism of phenol degradation.

Photocatalytic reduction of CO2 by graphitic carbon nitride polymers derived from urea and barbituric acid

Abstract: Conjugated carbon nitride nanosheets modified with barbituric acid (BA) were synthesized by a facile one-pot chemical condensation of urea. The obtained BA-modified carbon nitride samples were termed as CNU-BA X and were fully characterized by XRD, FTIR, XPS, NMR, EPR, FESEM, TEM, DRS, PL, BET and photocurrent measurements. The performance of the developed carbon nitride based semiconductors was investigated by applying them as polymeric photocatalysts for the reduction of CO 2 under visible light illumination. Results revealed that the copolymerization of urea with BA co-monomer strongly alternated the physical and chemical properties of carbon nitride polymer by improving optical absorption and creating surface molecular heterojunction that promoted charge separation, and consequently the enhanced photocatalytic performance was achieved. Various reaction parameters were investigated and optimized for the reaction system, and we found that under the optimal reaction condition, the best sample (CNU-BA 0.03 ) could effectively photocatalyze the CO 2 -to-CO conversion reaction with 15-fold-enhanced catalytic activity, compared to the non-modified sample derived from urea (named as CNU). Other typical comonomers were also selected to polymerize with urea to study the beneficial effect of copolymerization on the development of efficient carbon nitride based nanostructures for CO 2 photoreduction.

Visible-light-assisted aerobic photocatalytic oxidation of amines to imines over NH2-MIL-125(Ti)

Abstract: NH2-MIL-125(Ti), an amine-functionalized metal-organic-framework (MOF), was found for the first time to exhibit photocatalytic activity for the aerobic selective oxidation of amines to imines under visible light irradiations. Different amines can be effectively transformed to imines using O2 over NH2-MIL-125(Ti) under visible light irradiations. The photo-generated Ti3+ and .O2− which was formed via the reaction between Ti3+ and O2, are proposed to be involved in this transformation process based on the experimental observations and the ESR result. This work provides an economical, sustainable and green process for amines transformations and highlights the great potential of MOFs as photocatalysts for organic syntheses.

Iron-copper bimetallic nanoparticles embedded within ordered mesoporous carbon as effective and stable heterogeneous Fenton catalyst for the degradation of organic contaminants

Abstract: Iron-copper bimetallic nanoparticles embedded within ordered mesoporous carbon composite catalyst (CuFe-MC) was synthesized via a “one-pot” block-copolymer self-assembly strategy. The catalyst was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), etc. The results showed the catalyst was ordered 2D hexagonal mesostructure and iron-copper nanoparticles highly dispersed in the matrix of ordered mesoporous carbon. The composite was used as a heterogeneous Fenton catalyst and showed a promising application in the degradation of non-biodegradation organic contaminants. Eight organic compounds were chosen as model contaminants, such as phenol, bisphenol A (BPA), etc. Efficient total organic carbon (TOC) removal of each organic contaminant was achieved by using CuFe-MC as catalyst, which was higher than that by Fe2+ ion at the same reaction condition. BPA was selected to further investigate the high catalytic activity of CuFe-MC. CuFe-MC presented high adsorption capacity for BPA due to its high BET surface area (639 m2 g−1) and mesostructure. The results of BPA degradation showed that the catalytic activity of CuFe-MC was much higher than Fe-MC and Cu-MC. Electron spin resonance (ESR) and high performance liquid chromatography (HPLC) results indicated that the concentration of generated hydroxyl radicals (•OH) with CuFe-MC was much higher than Fe-MC and Cu-MC. The low iron leaching of CuFe-MC suggested its good stability. Moreover, it could be easily separated by using an external magnet after the reaction and remained good activity after being recycled for several times, demonstrating its promising long-term application in the treatment of wastewater.

Hierarchically Z-scheme photocatalyst of Ag@AgCl decorated on BiVO4 (040) with enhancing photoelectrochemical and photocatalytic performance

Abstract: Crystal facet dependence, as the crucial factor for semiconductor photocatalysis, is a significant strategy for optimizing the reactivity of photocatalyst. Given that there is a strong correlation between crystal facet and photocatalytic activity, we herein designed the Ag@AgCl core shell structure decorated on (040) crystal facet of BiVO4 (Ag@AgCl/BiVO4) as a hierarchical Z-scheme photocatalytic system by a simple route. In this hybridization system, the metallic Ag species not only act as the solid-state electron mediator, but can also absorb the photons from incident light and present the SPR-effect. As expected, such Ag@AgCl/BiVO4 heterostructure exhibits highly efficient photocatalytic performance and the first-order kinetic constant of photodegradation of Rhodamine B (RhB) is 300 times of pristine BiVO4. Moreover, by means of the EIS, LSV and l-t measurements, the Ag@AgCl/BiVO4 heterostructure also presents extraordinary photoelectrochemical performance. Focus is then given toward a novel perspective for understanding the mechanism of interfacial charge transfer of photocatalytic on the basis of the BiVO4-based all-solid-state Z-scheme photocatalyst. This work is expected to open up new insights into the architectural design of novel Z-scheme photocatalysts with high photoactivity and further utilization in the field of environmental or energy. (C) 2015 Elsevier B.V. All rights reserved.

The prevalence of surface oxygen vacancies over the mobility of bulk oxygen in nanostructured ceria for the total toluene oxidation

Abstract: This paper reveals the key importance of surface oxygen defects in the oxidation catalytic activity of nanostructured ceria. A series of nanostructured rods and cubes with different physico–chemical properties have been synthesized, characterized and tested in the total toluene oxidation. The variation of the temperature and base concentration during the hydrothermal syntheses of nanostructured ceria leads not only to different ceria morphologies with high shape purity, but also to structures with tuneable surface areas and defect concentrations. Ceria nanorods present a higher surface area and a higher concentration of bulk and surface defects than nanocubes associated with their exposed crystal planes, leading to high oxidation activities. However, for a given morphology, the catalytic activity for toluene oxidation is directly related to the concentration of surface oxygen defects and not the overall concentration of oxygen vacancies as previously believed.

Fabrication of sulfur-doped g-C3N4/Au/CdS Z-scheme photocatalyst to improve the photocatalytic performance under visible light

Abstract: Au and CdS nanoparticles were firstly deposited on the surface of g-CNS by two-step self-assembly process to afford sandwich-structured Z-scheme g-CNS/Au/CdS photocatalyst. The photocatalytic reduction of water to hydrogen was highly improved in lactic acid scavenger solution using the as-prepared g-CNS/Au/CdS than using g-CNS/CdS in the presence of visible light, and the photocatalytic degradation of RhB dye was also improved. According to the photoluminescence spectra and excited state electron radioactive decay lifetime, when Au was paired between g-CNS and CdS, based on the Z-scheme charge-carrier transfer mechanism, the redox ability of the photogenerated holes and electrons was enhanced, followed by the increased lifetime of the photoelectrons. Therefore, the photocatalytic ability of the g-CNS/Au/CdS composite was significantly improved.

Dry reforming of methane over CeO2 supported Ni, Co and Ni–Co catalysts

Abstract: Ceria supported Ni, Co monometallic and Ni–Co bimetallic catalysts were prepared by incipient wetness impregnation method, calcined at two different temperatures (700 °C and 900 °C) and tested for dry reforming of methane reaction at 700 °C. The activities of ceria-based Ni containing catalysts decreased with increasing calcination temperature accompanied by a decrease in coke deposition. While Ni/CeO 2 and Ni–Co/CeO 2 catalysts exhibited comparable high activities, Co/CeO 2 catalysts exhibited very low activity. The lower activity of Co/CeO 2 catalyst was attributed to strong metal support interaction (SMSI). The SMSI effect was confirmed with TEM images showing a layer of support coating the metal particles. The diversity of the deposited carbon structures in terms morphology (straight long filaments, highly entangled and curly shaped filaments, filaments with knuckle-like structure and carbon onions) was noted. In addition to the carbon buildup, the deactivation was observed to be due to the loss of active metals in the carbon filaments.

Enhanced catalytic activity of potassium-doped graphitic carbon nitride induced by lower valence position

Abstract: The potassium doped graphitic carbon nitride (K-C 3 N 4 ) photocatalysts were prepared via thermal polymerization of dicyandiamide and KI in atmosphere. The valence band (VB) position of g-C 3 N 4 was decreased via potassium doping, resulting in enhanced separation and immigration of photogenerated carriers under visible light. The optimum K-C 3 N 4 exhibited obviously enhanced photocatalytic activities for phenol and MB degradation, which were about 3.3 and 5.8 times as high as those of bulk g-C 3 N 4 , respectively. The photocatalytic activity of K-C 3 N 4 decreased with excessive KI mass fraction in the precursor due to the incomplete polymerization of g-C 3 N 4 .

Visible light activity of rare earth metal doped (Er3+, Yb3+ or Er3+/Yb3+) titania photocatalysts

Abstract: A series of Er3+-TiO2, Yb3+-TiO2 and Er3+/Yb3+-TiO2 photocatalysts were obtained via sol–gel method, using lanthanides precursor ranging from 0.25 to 10 mol%. The experiments demonstrated that phenol in aqueous solutions was successfully degraded under visible light (λ > 450 nm) using Er/Yb-TiO2. The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron emission spectroscopy (XPS), UV–vis absorption measurement, BET surface area analysis and luminescent spectroscopy. XPS analysis revealed that erbium and ytterbium were present in the form of oxides. The sample showing the highest photoactivity was in the form of anatase, its surface area equalled to 125 m2/g, average crystals size was 13 nm, and it was prepared introducing 1 mol% of Yb3+ into reaction medium. 3 h of irradiation resulted in 89% of phenol degradation under visible light. Action spectra analysis performed for the selected Er/Yb-TiO2 samples, revealed that irradiation from 420 to 475 nm is responsible for visible light photoactivity.

Graphene-modified nanosized Ag3PO4 photocatalysts for enhanced visible-light photocatalytic activity and stability

Abstract: Novel Ag3PO4 photocatalyst possesses high visible-light photocatalytic activity, but the large crystallite size and the photocorrosion severely limit its practical application. It is highly desirable to develop new Ag3PO4 photocatalytic systems with nanosized structure and good photocatalytic stability. In this work, we prepare new graphene-modified nanosized Ag3PO4 photocatalyst by in situ growth strategy in an organic solvent. The as-prepared nanosized Ag3PO4 particles–graphene composite exhibits enhanced visible-light photocatalytic activity and stability toward the degradation of methylene blue (MB) in aqueous solution compared with bare nanosized Ag3PO4 particles and conventional large-sized Ag3PO4 particles–graphene composite. This enhanced photocatalytic activity and stability arise from the positive synergetic effects of the nanosized Ag3PO4 particles and graphene sheets including an increase in the number of active adsorption sites, suppression of charge recombination, reducing the formation of Ag nanoparticles. This work shows a great potential of nanosized Ag3PO4 particles–graphene composite for environmental purification of organic pollutants.

Getting insight into the influence of SO2 on TiO2/CeO2 for the selective catalytic reduction of NO by NH3

Abstract: A series of inverse TiO2/CeO2 catalysts were prepared by the impregnation method and their catalytic performances for the selective catalytic reduction of NO by NH3 have been tested with and without SO2 and/or H2O. Compared with the normally discussed CeO2/TiO2 catalyst, the advantage of inverse TiO2/CeO2 catalyst was not only shown a good low temperature catalytic activity (150–250 °C), but also exhibited much better SO2 resistance performances with the existence of 200 ppm SO2 and/or 5 vol.% H2O at 300 °C. Furthermore, SO2 had more significant inhibitory effect on catalytic activity than H2O based on the configuration differences of Ce–Ti-based catalysts. These catalysts were investigated by means of TG-DTA, XRD, BET, in situ DRIFT, XPS and H2-TPR. The results demonstrated that the sulfation of these samples under reactive conditions mainly generated three different kinds of sulfate species including NH4HSO4, surface and bulk-like metal sulfates (mainly interacted with cerium species). The formed metal sulfates blocked the active sites of Ce–O–Ti and resulted in the deactivation of CeO2/TiO2. Although metal sulfates were also formed over TiO2/CeO2, NH3-SCR could still proceed and that was similar as the reaction system with the use of sulfated CeO2 as the catalyst. Meanwhile, the interactions between SO2 and Ce–Ti-based catalysts were discussed in detail and an adsorption model of SO2 was proposed.

Noble-metal-free MoS2 co-catalyst decorated UiO-66/CdS hybrids for efficient photocatalytic H2 production

Abstract: A novel and highly efficient photocatalyst MoS 2 /UiO-66/CdS has been fabricated through dual modification of CdS with metal-organic framework (MOF) UiO-66 and MoS 2 . UiO-66 was firstly introduced as a matrix for the well-dispersed growth of CdS, resulting in large active surface area. Moreover, the heterojunction between UiO-66 and CdS promoted the separation of photogenerated electron–hole pairs. MoS 2 as cocatalyst was further deposited on UiO-66/CdS via a facile photo-assisted approach. This technique made CdS, UiO-66 and MoS 2 undergo an intimate interfacial interaction, setting a stage for rapid transfer of photogenerated electrons between the components of the composite, and hence dramatically increased the synergetic catalytic effect of UiO-66, MoS 2 and CdS. Without a noble-metal cocatalyst, the obtained MoS 2 /UiO-66/CdS composites functioned as high-performance photocatalysts for H 2 evolution under visible light irradiation. An unusual H 2 production rate of 650 μmol h −1 has been reached by the sample of MoS 2 /UiO-66/CdS when the content of UiO-66 is 50 wt% and MoS 2 is 1.5 wt%. This is nearly 60 times higher than the H 2 evolution rate with pure CdS and also exceeds that of Pt/UiO-66/CdS under the same reaction conditions. More importantly, in sharp contrast with the obvious deterioration in photoactivity of pure CdS, the MoS 2 /UiO-66/CdS displayed significantly enhanced photostability. This study clearly demonstrates the benefit of using MOFs as ideal support and MoS 2 as cocatalyst to work cooperatively for enhancing the photocatalytic H 2 evolution activity and stability of semiconductors.