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2017 Volume 38 Issue 6
2017, 38(6):
Abstract:
2017, 38(6): 949-950
doi: 10.1016/S1872-2067(17)62851-1
Abstract:
2017, 38(6): 951-969
doi: 10.1016/S1872-2067(17)62801-8
Abstract:
The quest for low-cost yet efficient non-Pt electrocatalysts for the oxygen reduction reaction (ORR) has become one of the main focuses of research in the field of catalysis, which has implications for the development of the next generation of greener fuel cells. Here, we comprehensively describe the ‘big picture’ of recent advances made in the rational design of ORR electrocatalysts, including molecule-based, metal-oxide-based, metal-nanomaterial-based and two-dimensional electrocatalysts. Transition metals can fabricate molecular electrocatalysts with N4-macrocycles such as porphyrin-class compounds and the so-formed M-N-C active centre plays a crucial role in determining the catalytic performances towards the ORR. Group-IV and-V Transition metal oxides represent another class of promising alternative of Pt-based catalysts for the ORR which catalytic activity largely depends on the surface structure and the introduction of surface defects. Recent advances in synthesis of metallic nanoparticles (NPs) allow for precise control over particle sizes and shapes and the crystalline facets exposed to enhance the ORR performance of electrocatalysts. Two-dimensional materials such as functionalized grapheme or MoS2 are emerging as novel electrocatalysts for the ORR. This review covers various aspects towards the design of future ORR electrocatalysts, including the catalytic performance, stability, durability and cost. Some novel electrocatalysts even surpass commercial Pt/C systems, demonstrating their potential to be alternatives in industrial applications. Despite the encouraging progress, challenges, which are also described, remain to be overcome before the real-world application of novel ORR electrocatalysts.
The quest for low-cost yet efficient non-Pt electrocatalysts for the oxygen reduction reaction (ORR) has become one of the main focuses of research in the field of catalysis, which has implications for the development of the next generation of greener fuel cells. Here, we comprehensively describe the ‘big picture’ of recent advances made in the rational design of ORR electrocatalysts, including molecule-based, metal-oxide-based, metal-nanomaterial-based and two-dimensional electrocatalysts. Transition metals can fabricate molecular electrocatalysts with N4-macrocycles such as porphyrin-class compounds and the so-formed M-N-C active centre plays a crucial role in determining the catalytic performances towards the ORR. Group-IV and-V Transition metal oxides represent another class of promising alternative of Pt-based catalysts for the ORR which catalytic activity largely depends on the surface structure and the introduction of surface defects. Recent advances in synthesis of metallic nanoparticles (NPs) allow for precise control over particle sizes and shapes and the crystalline facets exposed to enhance the ORR performance of electrocatalysts. Two-dimensional materials such as functionalized grapheme or MoS2 are emerging as novel electrocatalysts for the ORR. This review covers various aspects towards the design of future ORR electrocatalysts, including the catalytic performance, stability, durability and cost. Some novel electrocatalysts even surpass commercial Pt/C systems, demonstrating their potential to be alternatives in industrial applications. Despite the encouraging progress, challenges, which are also described, remain to be overcome before the real-world application of novel ORR electrocatalysts.
2017, 38(6): 970-990
doi: 10.1016/S1872-2067(17)62818-3
Abstract:
Yolk-shell structured nanoparticles are of immense scientific and technological interests because of their unique architecture and myriad of applications. This review summarizes recent progresses in the use of yolk-shell structured nanoparticles as nanoreactors for various chemical reactions. A very brief overview of synthetic strategies is provided with emphasis on recent research progress in the last five years. Catalytic applications of these yolk-shell structured nanoreactors are then discussed by covering photocatalysis, methane reforming and electrochemical conversion. The state of the art research and perspective in future development are also highlighted.
Yolk-shell structured nanoparticles are of immense scientific and technological interests because of their unique architecture and myriad of applications. This review summarizes recent progresses in the use of yolk-shell structured nanoparticles as nanoreactors for various chemical reactions. A very brief overview of synthetic strategies is provided with emphasis on recent research progress in the last five years. Catalytic applications of these yolk-shell structured nanoreactors are then discussed by covering photocatalysis, methane reforming and electrochemical conversion. The state of the art research and perspective in future development are also highlighted.
2017, 38(6): 991-1005
doi: 10.1016/S1872-2067(17)62810-9
Abstract:
The generation of hydrogen through the electrolysis of water has attracted attention as a promising way to produce and store energy using renewable energy sources. In this process, a catalyst is very important to achieve a high-energy conversion efficiency for the electrolysis of water. A good catalyst for water electrolysis should exhibit high catalytic activity, good stability, low cost and good scalability. Much research has been devoted to developing efficient catalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Traditionally, it has been accepted that a material with high crystallinity is important to serve as a good catalyst for HER and/or OER. Recently, catalysts for HER and/or OER in the electrolysis of water splitting based on amorphous materials have received much interest in the scientific community owing to the abundant unsaturated active sites on the amorphous surface, which form catalytic centers for the reaction of the electrolysis of water. We summarize the recent advances of amorphous catalysts for HER, OER and overall water splitting by electrolysis and the related fundamental chemical reactions involved in the electrolysis of water. The current challenges confronting the electrolysis of water and the development of more efficient amorphous catalysts are also discussed.
The generation of hydrogen through the electrolysis of water has attracted attention as a promising way to produce and store energy using renewable energy sources. In this process, a catalyst is very important to achieve a high-energy conversion efficiency for the electrolysis of water. A good catalyst for water electrolysis should exhibit high catalytic activity, good stability, low cost and good scalability. Much research has been devoted to developing efficient catalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Traditionally, it has been accepted that a material with high crystallinity is important to serve as a good catalyst for HER and/or OER. Recently, catalysts for HER and/or OER in the electrolysis of water splitting based on amorphous materials have received much interest in the scientific community owing to the abundant unsaturated active sites on the amorphous surface, which form catalytic centers for the reaction of the electrolysis of water. We summarize the recent advances of amorphous catalysts for HER, OER and overall water splitting by electrolysis and the related fundamental chemical reactions involved in the electrolysis of water. The current challenges confronting the electrolysis of water and the development of more efficient amorphous catalysts are also discussed.
2017, 38(6): 1006-1010
doi: 10.1016/S1872-2067(17)62764-5
Abstract:
High active and cost-effective electrocatalysts for the oxygen reduction reaction (ORR) are essential components of renewable energy technologies, such as fuel cells and metal/air batteries. Herein, we propose that ORR active Cu/graphitic carbon nitride (Cu/g-CN) electrocatalyst can be prepared via a facile hydrothermal reaction in the present of the ionic liquid (IL) bis(1-hexadecyl-3- methylimidazolium) tetrachlorocuprate [(C16mim)2CuCl4] and protonated g-CN. The as-prepared Cu/g-CN showed an impressive ORR catalytic activity that a 99 mV positive shift of the onset potential and 2 times kinetic current density can be clearly observed, comparing with the pure g-CN. In addition, the Cu/g-CN revealed better stability and methanol tolerance than commercial Pt/C (HiSPECTM 3000, 20%). Therefore, the proposed Cu/g-CN, as the inexpensive and efficient ORR electrocatalyst, would be a potential candidate for application in fuel cells.
High active and cost-effective electrocatalysts for the oxygen reduction reaction (ORR) are essential components of renewable energy technologies, such as fuel cells and metal/air batteries. Herein, we propose that ORR active Cu/graphitic carbon nitride (Cu/g-CN) electrocatalyst can be prepared via a facile hydrothermal reaction in the present of the ionic liquid (IL) bis(1-hexadecyl-3- methylimidazolium) tetrachlorocuprate [(C16mim)2CuCl4] and protonated g-CN. The as-prepared Cu/g-CN showed an impressive ORR catalytic activity that a 99 mV positive shift of the onset potential and 2 times kinetic current density can be clearly observed, comparing with the pure g-CN. In addition, the Cu/g-CN revealed better stability and methanol tolerance than commercial Pt/C (HiSPECTM 3000, 20%). Therefore, the proposed Cu/g-CN, as the inexpensive and efficient ORR electrocatalyst, would be a potential candidate for application in fuel cells.
2017, 38(6): 1011-1020
doi: 10.1016/S1872-2067(17)62765-7
Abstract:
The exploration of highly active and durable cathodic oxygen reduction reaction (ORR) catalysts with economical production cost is still the bottleneck to realize the large-scale commercialization of fuel cells and metal-air batteries. Given that carbon support is crucial to the electrocatalysts, and Pt is the best-known ORR catalyst so far, in this work, we employed a simple impregnation method for synthesizing a kind of defective activated carbon (D-AC) supported low Pt content electrocatalysts for the ORR. The reduction conditions of the Pt-containing precursor were firstly optimized, and the influence of the Pt loading amount on the ORR was investigated as well. The results show that the obtained D-AC@5.0%Pt sample (contains 5 wt% Pt) has surpassed the commercial Pt/C with 20 wt% Pt for the ORR in an alkaline solution. In the meantime, it is more stable than the commercial Pt/C. The outstanding ORR performance of the D-AC@5.0%Pt confirms that both the unique defects in the D-AC and the introduced Pt particles are indispensable to the ORR. Particularly, the ORR activity of the synthesized catalysts is superior to most of the reported counterparts, but with much easier preparation methods and lower production cost, making them more advantageous in practical fuel cell applications.
The exploration of highly active and durable cathodic oxygen reduction reaction (ORR) catalysts with economical production cost is still the bottleneck to realize the large-scale commercialization of fuel cells and metal-air batteries. Given that carbon support is crucial to the electrocatalysts, and Pt is the best-known ORR catalyst so far, in this work, we employed a simple impregnation method for synthesizing a kind of defective activated carbon (D-AC) supported low Pt content electrocatalysts for the ORR. The reduction conditions of the Pt-containing precursor were firstly optimized, and the influence of the Pt loading amount on the ORR was investigated as well. The results show that the obtained D-AC@5.0%Pt sample (contains 5 wt% Pt) has surpassed the commercial Pt/C with 20 wt% Pt for the ORR in an alkaline solution. In the meantime, it is more stable than the commercial Pt/C. The outstanding ORR performance of the D-AC@5.0%Pt confirms that both the unique defects in the D-AC and the introduced Pt particles are indispensable to the ORR. Particularly, the ORR activity of the synthesized catalysts is superior to most of the reported counterparts, but with much easier preparation methods and lower production cost, making them more advantageous in practical fuel cell applications.
2017, 38(6): 1021-1027
doi: 10.1016/S1872-2067(17)62811-0
Abstract:
Water oxidation is one of the most attractive techniques for intermittent renewable energy conversion and storage. The oxygen evolution electrocatalytic performance of an amorphous Co-B alloy and its derivatives were studied. These materials were chemically synthesized by reducing a Co salt with NaBH4. The amorphous Co-B alloy showed good electrocatalytic activity in oxygen evolution but its stability was poor. A hydrotalcite-wrapped Co-B alloy was synthesized by mild oxidation. The electrocatalytic activity of this material in the oxygen evolution reaction was better than that of a commercially available Ir/C catalyst.
Water oxidation is one of the most attractive techniques for intermittent renewable energy conversion and storage. The oxygen evolution electrocatalytic performance of an amorphous Co-B alloy and its derivatives were studied. These materials were chemically synthesized by reducing a Co salt with NaBH4. The amorphous Co-B alloy showed good electrocatalytic activity in oxygen evolution but its stability was poor. A hydrotalcite-wrapped Co-B alloy was synthesized by mild oxidation. The electrocatalytic activity of this material in the oxygen evolution reaction was better than that of a commercially available Ir/C catalyst.
2017, 38(6): 1028-1037
doi: 10.1016/S1872-2067(17)62830-4
Abstract:
Ultrathin small MoS2 nanosheets exhibit a higher electrocatalytic activity for the hydrogen evolution reaction. However, strong interactions between MoS2 layers may result in aggregation; together with the low conductivity of MoS2, this may lower its electrocatalytic activity. In this paper we present a method that we developed to directly produce solid S, N co-doped carbon (SNC) with a graphite structure and multiple surface groups through a hydrothermal route. When Na2MoO4 was added to the reaction, polymolybdate could be anchored into the carbon materials via a chemical interaction that helps polymolybdate disperse uniformly into the SNC. After a high temperature treatment, polymolybdate transformed into MoS2 at 800 ℃ for 6 h in a N2 atmosphere at a heating rate of 5 ℃/min, owing to S2- being released from the SNC during the treatment (denoted as MoS2/SNC-800-6h). The SNC effectively prevents MoS2 from aggregating into large particles, and we successfully prepared highly dispersed MoS2 in the SNC matrix. Electrochemical characterizations indicate that MoS2/SNC-900-12h exhibits a low onset potential of 115 mV and a low overpotential of 237 mV at a current density of 10 mA/cm2. Furthermore, MoS2/SNC-900-12h also had an excellent stability with only ~2.6% decay at a current density of 10 mA/cm2 after 5000 test cycles.
Ultrathin small MoS2 nanosheets exhibit a higher electrocatalytic activity for the hydrogen evolution reaction. However, strong interactions between MoS2 layers may result in aggregation; together with the low conductivity of MoS2, this may lower its electrocatalytic activity. In this paper we present a method that we developed to directly produce solid S, N co-doped carbon (SNC) with a graphite structure and multiple surface groups through a hydrothermal route. When Na2MoO4 was added to the reaction, polymolybdate could be anchored into the carbon materials via a chemical interaction that helps polymolybdate disperse uniformly into the SNC. After a high temperature treatment, polymolybdate transformed into MoS2 at 800 ℃ for 6 h in a N2 atmosphere at a heating rate of 5 ℃/min, owing to S2- being released from the SNC during the treatment (denoted as MoS2/SNC-800-6h). The SNC effectively prevents MoS2 from aggregating into large particles, and we successfully prepared highly dispersed MoS2 in the SNC matrix. Electrochemical characterizations indicate that MoS2/SNC-900-12h exhibits a low onset potential of 115 mV and a low overpotential of 237 mV at a current density of 10 mA/cm2. Furthermore, MoS2/SNC-900-12h also had an excellent stability with only ~2.6% decay at a current density of 10 mA/cm2 after 5000 test cycles.
2017, 38(6): 1038-1044
doi: 10.1016/S1872-2067(17)62780-3
Abstract:
In the present study, porous bulk palladium samples were prepared by sodium chloride salt powder spacer incorporation and removal combined with dealloying. The obtained porous Pd bulks were characterized by X-ray diffraction, field-emission scanning electron microscopy and N2 adsorption isotherm measurements. The prepared porous Pd bulk samples showed a hierarchical pore structure, a high porosity of ~88%, a high surface area of ~54 m2/g, and a compression strength of ~0.5 MPa. Electrochemical measurements were performed to evaluate the electrocatalytic properties of the porous Pd bulk samples, revealing their effectiveness for ethanol oxidation.
In the present study, porous bulk palladium samples were prepared by sodium chloride salt powder spacer incorporation and removal combined with dealloying. The obtained porous Pd bulks were characterized by X-ray diffraction, field-emission scanning electron microscopy and N2 adsorption isotherm measurements. The prepared porous Pd bulk samples showed a hierarchical pore structure, a high porosity of ~88%, a high surface area of ~54 m2/g, and a compression strength of ~0.5 MPa. Electrochemical measurements were performed to evaluate the electrocatalytic properties of the porous Pd bulk samples, revealing their effectiveness for ethanol oxidation.
2017, 38(6): 1045-1051
doi: 10.1016/S1872-2067(17)62809-2
Abstract:
An amorphous ferric oxide layer was prepared on a bismuth vanadate photoanode. This resulted in improved charge carrier separation and surface catalytic performance compared with the photoanode without the oxide layer. The photocurrent of the oxide-layer-containing photoanode was 2.52 mA/cm2 at 1.23 V versus the reversible hydrogen electrode, in potassium phosphate buffer (0.5 mol/L, pH = 7.0). The amorphous ferric oxide layer on the photoanode contained low-valence-state iron species (FeII), which enabled efficient hole extraction and transfer.
An amorphous ferric oxide layer was prepared on a bismuth vanadate photoanode. This resulted in improved charge carrier separation and surface catalytic performance compared with the photoanode without the oxide layer. The photocurrent of the oxide-layer-containing photoanode was 2.52 mA/cm2 at 1.23 V versus the reversible hydrogen electrode, in potassium phosphate buffer (0.5 mol/L, pH = 7.0). The amorphous ferric oxide layer on the photoanode contained low-valence-state iron species (FeII), which enabled efficient hole extraction and transfer.
2017, 38(6): 1052-1062
doi: 10.1016/S1872-2067(17)62845-6
Abstract:
Magnetically separable bismuth ferrite (BiFeO3) nanoparticles were fabricated by a citrate self-combustion method and coated with titanium dioxide (TiO2) by hydrolysis of titanium butoxide (Ti(OBu)4) to form BiFeO3@TiO2 core-shell nanocomposites with different mass ratios of TiO2 to BiFeO3. The photocatalytic performance of the catalysts was comprehensively investigated via photocatalytic oxidation of methyl violet (MV) under both ultraviolet and visible-light irradiation. The BiFeO3@TiO2 samples exhibited better photocatalytic performance than either BiFeO3 or TiO2 alone, and a BiFeO3@TiO2 sample with a mass ratio of 1:1 and TiO2 shell thickness of 50-100 nm showed the highest photo-oxidation activity of the catalysts. The enhanced photocatalytic activity was ascribed to the formation of a p-n junction of BiFeO3 and TiO2 with high charge separation efficiency as well as strong light absorption ability. Photoelectrochemical Mott-Schottky (MS) measurements revealed that both the charge carrier transportation and donor density of BiFeO3 were markedly enhanced after introduction of TiO2. The mechanism of MV degradation is mainly attributed to hydroxyl radicals and photogenerated electrons based on energy band theory and the formation of an internal electrostatic field. In addition, the unique core-shell structure of BiFeO3@TiO2 also promotes charge transfer at the BiFeO3/TiO2 interface by increasing the contact area between BiFeO3 and TiO2. Finally, the photocatalytic activity of BiFeO3@TiO2 was further confirmed by degradation of other industrial dyes under visible-light irradiation.
Magnetically separable bismuth ferrite (BiFeO3) nanoparticles were fabricated by a citrate self-combustion method and coated with titanium dioxide (TiO2) by hydrolysis of titanium butoxide (Ti(OBu)4) to form BiFeO3@TiO2 core-shell nanocomposites with different mass ratios of TiO2 to BiFeO3. The photocatalytic performance of the catalysts was comprehensively investigated via photocatalytic oxidation of methyl violet (MV) under both ultraviolet and visible-light irradiation. The BiFeO3@TiO2 samples exhibited better photocatalytic performance than either BiFeO3 or TiO2 alone, and a BiFeO3@TiO2 sample with a mass ratio of 1:1 and TiO2 shell thickness of 50-100 nm showed the highest photo-oxidation activity of the catalysts. The enhanced photocatalytic activity was ascribed to the formation of a p-n junction of BiFeO3 and TiO2 with high charge separation efficiency as well as strong light absorption ability. Photoelectrochemical Mott-Schottky (MS) measurements revealed that both the charge carrier transportation and donor density of BiFeO3 were markedly enhanced after introduction of TiO2. The mechanism of MV degradation is mainly attributed to hydroxyl radicals and photogenerated electrons based on energy band theory and the formation of an internal electrostatic field. In addition, the unique core-shell structure of BiFeO3@TiO2 also promotes charge transfer at the BiFeO3/TiO2 interface by increasing the contact area between BiFeO3 and TiO2. Finally, the photocatalytic activity of BiFeO3@TiO2 was further confirmed by degradation of other industrial dyes under visible-light irradiation.
2017, 38(6): 1063-1071
doi: 10.1016/S1872-2067(17)62806-7
Abstract:
Ag2O has attracted much recent attention, because of its high photocatalytic activity in the ultraviolet (UV)-visible region. However, there have been few reports on the near-infrared (NIR) photocatalytic activity of Ag2O. This paper reports the high NIR photocatalytic activity of Ag2O nanoparticles. Ag2O is unsuitable for application in full-solar-spectrum photocatalysis, because it is unstable under UV irradiation. A surface sulfurization process was carried out to address this issue. Specifically, a layer of Ag2S2O7 nanoparticles was grown on the surface of the Ag2O nanoparticles, to improve the stability of the Ag2O photocatalyst and enhance its photocatalytic activity in the UV, visible and NIR regions. The Ag2O/Ag2S2O7 heterostructure is a stable and efficient full-solar-spectrum photocatalyst. It has potential application in the photodegradation of organic pollutants, and more generally in environmental engineering where full utilization of the solar spectrum is required.
Ag2O has attracted much recent attention, because of its high photocatalytic activity in the ultraviolet (UV)-visible region. However, there have been few reports on the near-infrared (NIR) photocatalytic activity of Ag2O. This paper reports the high NIR photocatalytic activity of Ag2O nanoparticles. Ag2O is unsuitable for application in full-solar-spectrum photocatalysis, because it is unstable under UV irradiation. A surface sulfurization process was carried out to address this issue. Specifically, a layer of Ag2S2O7 nanoparticles was grown on the surface of the Ag2O nanoparticles, to improve the stability of the Ag2O photocatalyst and enhance its photocatalytic activity in the UV, visible and NIR regions. The Ag2O/Ag2S2O7 heterostructure is a stable and efficient full-solar-spectrum photocatalyst. It has potential application in the photodegradation of organic pollutants, and more generally in environmental engineering where full utilization of the solar spectrum is required.
2017, 38(6): 1072-1078
doi: 10.1016/S1872-2067(17)62850-X
Abstract:
One of the most general methods to enhance the separation of photogenerated carriers for g-C3N4 is to construct a suitable heterojunctional composite, according to the principle of matching energy levels. The interface contact in the fabricated nanocomposite greatly influences the charge transfer and separation so as to determine the final photocatalytic activities. However, the role of interface contact is often neglected, and is rarely reported to date. Hence, it is possible to further enhance the photocatalytic activity of g-C3N4-based nanocomposite by improving the interfacial connection. Herein, phosphate-oxygen (P-O) bridged TiO2/g-C3N4 nanocomposites were successfully synthesized using a simple wet chemical method, and the effects of the P-O functional bridges on the photogenerated charge separation and photocatalytic activity for pollutant degradation and CO2 reduction were investigated. The photocatalytic activity of g-C3N4 was greatly improved upon coupling with an appropriate amount of nanocrystalline TiO2, especially with P-O bridged TiO2. Atmosphere-controlled steady-state surface photovoltage spectroscopy and photoluminescence spectroscopy analyses revealed clearly the enhancement of photogenerated charge separation of g-C3N4 upon coupling with the P-O bridged TiO2, resulting from the built P-O bridges between TiO2 and g-C3N4 so as to promote effective transfer of excited electrons from g-C3N4 to TiO2. This enhancement was responsible for the improved photoactivity of the P-O bridged TiO2/g-C3N4 nanocomposite, which exhibited three-time photocatalytic activity enhancement for 2,4-dichlorophenol degradation and CO2 reduction compared with bare g-C3N4. Furthermore, radical-trapping experiments revealed that the ·OH species formed as hole-modulated direct intermediates dominated the photocatalytic degradation of 2,4-dichlorophenol. This work provides a feasible strategy for the design and synthesis of high-performance g-C3N4-based nanocomposite photocatalysts for pollutant degradation and CO2 reduction.
One of the most general methods to enhance the separation of photogenerated carriers for g-C3N4 is to construct a suitable heterojunctional composite, according to the principle of matching energy levels. The interface contact in the fabricated nanocomposite greatly influences the charge transfer and separation so as to determine the final photocatalytic activities. However, the role of interface contact is often neglected, and is rarely reported to date. Hence, it is possible to further enhance the photocatalytic activity of g-C3N4-based nanocomposite by improving the interfacial connection. Herein, phosphate-oxygen (P-O) bridged TiO2/g-C3N4 nanocomposites were successfully synthesized using a simple wet chemical method, and the effects of the P-O functional bridges on the photogenerated charge separation and photocatalytic activity for pollutant degradation and CO2 reduction were investigated. The photocatalytic activity of g-C3N4 was greatly improved upon coupling with an appropriate amount of nanocrystalline TiO2, especially with P-O bridged TiO2. Atmosphere-controlled steady-state surface photovoltage spectroscopy and photoluminescence spectroscopy analyses revealed clearly the enhancement of photogenerated charge separation of g-C3N4 upon coupling with the P-O bridged TiO2, resulting from the built P-O bridges between TiO2 and g-C3N4 so as to promote effective transfer of excited electrons from g-C3N4 to TiO2. This enhancement was responsible for the improved photoactivity of the P-O bridged TiO2/g-C3N4 nanocomposite, which exhibited three-time photocatalytic activity enhancement for 2,4-dichlorophenol degradation and CO2 reduction compared with bare g-C3N4. Furthermore, radical-trapping experiments revealed that the ·OH species formed as hole-modulated direct intermediates dominated the photocatalytic degradation of 2,4-dichlorophenol. This work provides a feasible strategy for the design and synthesis of high-performance g-C3N4-based nanocomposite photocatalysts for pollutant degradation and CO2 reduction.
2017, 38(6): 1079-1086
doi: 10.1016/S1872-2067(17)62820-1
Abstract:
Solar-driven thermochemical water splitting represents one efficient route to the generation of H2 as a clean and renewable fuel. Due to their outstanding catalytic abilities and promising solar fuel production capacities, perovskite-type redox catalysts have attracted significant attention in this regard. In the present study, the perovskite series La1-xCaxMn1-yAlyO3 (x, y = 0.2, 0.4, 0.6, or 0.8) was fabricated using a modified Pechini method and comprehensively investigated to determine the applicability of these materials to solar H2 production via two-step thermochemical water splitting. The thermochemical redox behaviors of these perovskites were optimized by doping at either the A (Ca) or B (Al) sites over a broad range of substitution values, from 0.2 to 0.8. Through this doping, a highly efficient perovskite (La0.6Ca0.4Mn0.6Al0.4O3) was developed, which yielded a remarkable H2 production rate of 429 μmol/g during two-step thermochemical H2O splitting, going between 1400 and 1000 ℃. Moreover, the performance of the optimized perovskite was found to be eight times higher than that of the benchmark catalyst CeO2 under the same experimental conditions. Furthermore, these perovskites also showed impressive catalytic stability during two-step thermochemical cycling tests. These newly developed La1-xCaxMn1-yAlyO3 redox catalysts appear to have great potential for future practical applications in thermochemical solar fuel production.
Solar-driven thermochemical water splitting represents one efficient route to the generation of H2 as a clean and renewable fuel. Due to their outstanding catalytic abilities and promising solar fuel production capacities, perovskite-type redox catalysts have attracted significant attention in this regard. In the present study, the perovskite series La1-xCaxMn1-yAlyO3 (x, y = 0.2, 0.4, 0.6, or 0.8) was fabricated using a modified Pechini method and comprehensively investigated to determine the applicability of these materials to solar H2 production via two-step thermochemical water splitting. The thermochemical redox behaviors of these perovskites were optimized by doping at either the A (Ca) or B (Al) sites over a broad range of substitution values, from 0.2 to 0.8. Through this doping, a highly efficient perovskite (La0.6Ca0.4Mn0.6Al0.4O3) was developed, which yielded a remarkable H2 production rate of 429 μmol/g during two-step thermochemical H2O splitting, going between 1400 and 1000 ℃. Moreover, the performance of the optimized perovskite was found to be eight times higher than that of the benchmark catalyst CeO2 under the same experimental conditions. Furthermore, these perovskites also showed impressive catalytic stability during two-step thermochemical cycling tests. These newly developed La1-xCaxMn1-yAlyO3 redox catalysts appear to have great potential for future practical applications in thermochemical solar fuel production.
2017, 38(6): 1087-1100
doi: 10.1016/S1872-2067(17)62813-4
Abstract:
The use of H2SO4-, HCl-, H3PO4-, and CH3COOH-activated montmorillonite (Mt) and WOx/H3PO4- activated Mt as catalysts for the gas-phase dehydration of glycerol was investigated. The WOx/H3PO4-activated Mt catalysts were prepared by an impregnation method using H3PO4-activated Mt (Mt-P) as the support. The catalysts were characterized using powder X-ray diffraction, Fourier-transform infrared spectroscopy, N2 adsorption-desorption, diffuse reflectance ultraviolet-visible spectroscopy, temperature-programmed desorption of NH3, and thermogravimetric analysis. The acid activation of Mt and WOx loaded on Mt-P affected the strength and number of acid sites arising from H+ exchange, the leaching of octahedral Al3+ cations from Mt octahedral sheets, and the types of WOx (2.7 ≤ x ≤ 3) species (i.e., isolated WO4/WO6-containing clusters, two-dimensional [WO6] polytungstates, or three-dimensional WO3 crystals). The strong acid sites were weakened, and the weak and medium acid sites were strengthened when the W loading on Mt-P was 12 wt% (12%W/Mt-P). The 12%W/Mt-P catalyst showed the highest catalytic activity. It gave a glycerol conversion of 89.6% and an acrolein selectivity of 81.8% at 320 ℃. Coke deposition on the surface of the catalyst led to deactivation.
The use of H2SO4-, HCl-, H3PO4-, and CH3COOH-activated montmorillonite (Mt) and WOx/H3PO4- activated Mt as catalysts for the gas-phase dehydration of glycerol was investigated. The WOx/H3PO4-activated Mt catalysts were prepared by an impregnation method using H3PO4-activated Mt (Mt-P) as the support. The catalysts were characterized using powder X-ray diffraction, Fourier-transform infrared spectroscopy, N2 adsorption-desorption, diffuse reflectance ultraviolet-visible spectroscopy, temperature-programmed desorption of NH3, and thermogravimetric analysis. The acid activation of Mt and WOx loaded on Mt-P affected the strength and number of acid sites arising from H+ exchange, the leaching of octahedral Al3+ cations from Mt octahedral sheets, and the types of WOx (2.7 ≤ x ≤ 3) species (i.e., isolated WO4/WO6-containing clusters, two-dimensional [WO6] polytungstates, or three-dimensional WO3 crystals). The strong acid sites were weakened, and the weak and medium acid sites were strengthened when the W loading on Mt-P was 12 wt% (12%W/Mt-P). The 12%W/Mt-P catalyst showed the highest catalytic activity. It gave a glycerol conversion of 89.6% and an acrolein selectivity of 81.8% at 320 ℃. Coke deposition on the surface of the catalyst led to deactivation.
