In the twenty-first century, global warming and energy shortage have become major global issues. Up to now, the utilization of CO
2
as a carbon source for the production of fuels and chemicals has ...received increased attention. The photocatalytic reduction of CO
2
into solar fuels has turned out to become one of the most promising and environmentally friendly methods. Well-defined heterojunction structures between two semiconductors with matching electronic band structures can effectively facilitate charge transfer and suppress the recombination of photogenerated electrons and holes, resulting in enhanced photocatalytic performance. This review focuses on the design and fabrication of TiO
2
-based heterojunction photocatalysts and their recent progresses into developing solar fuels
via
the photocatalytic reduction of CO
2
. The photocatalytic performances of a number of typical TiO
2
-based heterojunction photocatalysts,
e.g.
, p-n, non-p-n, Z-scheme, TiO
2
-metal, TiO
2
-carbon, phase, facet, and other heterojunctions, are summarized and analyzed. The reaction mode and some typical photoreactors,
e.g.
, slurry photoreactor, optical-fiber photoreactor, monolith photoreactor, and optofluidic microreactor, are also presented and analyzed. In the end, we propose a perspective on the opportunities and challenges to design new types of photocatalysts and photoreactors for improving the photocatalytic reduction of CO
2
.
Recent advances in the photocatalytic reduction of CO
2
into solar fuels using TiO
2
-based heterojunction photocatalysts have been highlighted.
With increasing pollution of water resources and demand for hydrogen energy, photocatalysis, as a "green chemistry" technology, has attracted great attention. To meet the practical application ...requirements, photocatalysts should possess enhanced efficiency and be of low cost. Here, a novel Z-scheme ternary ZnTiO3/Zn2Ti3O8/ZnO heterojunction has been prepared by a solvothermal-calcination process. The phase transformation process of the sample can be defined as two processes, dehydration and thermal decomposition (ZnTiO3 → Zn2Ti3O8 + ZnO). The ZnTiO3/Zn2Ti3O8/ZnO heterojunction produced in this facile phase transformation strategy displayed highly efficient photocatalytic performance in water splitting for hydrogen production and pollutant removal, e.g. phenol, dye, and heavy metal Cr(vi). On the basis of the PL spectra, photocurrent response, radical trapping experiments and ESR tests, we found that a nontraditional transport of photoinduced carriers created by a single Z-scheme mechanism played a significant role in the efficient removing of target pollutants and hydrogen generation. This work provides a facile phase transformation approach to construct a Z-scheme semiconductor heterostructure system with high efficiency for hydrogen production and water pollution treatment.
The conversion of biomass-derived molecules into adipic acid represents a highly attractive green route for sustainable production of adipic acid, a key monomer of nylon 66 and polyurethane. Here, we ...report the direct synthesis of adipic acid from 2,5-furandicarboxylic acid, which can be obtained from cellulose-based 5-hydroxymethylfurfural, using a niobic acid-supported platinum catalyst under hydrogen in water.
Biomass-derived 2,5-furandicarboxylic acid was successfully converted to adipic acid over a niobic acid-supported Pt catalyst in water under H
2
.
The solar energy-driven reduction of CO2 and H2O to syngas (H2/CO), an important platform to produce chemicals, is of significance for alleviating greenhouse gas emission and utilizing sustainable ...solar energy. Here, we report a facile method for the photoelectrocatalytic reduction of CO2 and H2O to syngas over an Ag nanoparticle (NP) modified p-Si nanowire array catalyst. The particle size of Ag significantly influences the activity of CO2 reduction to CO. The H2/CO molar ratio in reduction products can be tuned in the range from 1 to 4 by controlling the size of Ag NPs from 4.2 to 16 nm. The adsorption strength of CO on the catalyst was found to decline with the increase in the size of Ag NPs. The Ag NPs of 8.2 nm, which possess a moderate CO adsorption strength, exhibit the maximum production of CO with the H2/CO ratio of 2/1.
•A novel AgI/Ag2CO3 heterojunction was prepared via coprecipitation process.•AgI/Ag2CO3 heterojunction increase e−/h+ pairs separation.•The production of •OH and O2•− radicals was promoted.•High ...photocatalytic activity and stability were obtained over AgI/Ag2CO3.
An insurmountable problem for silver-based semiconductor photocatalysts is their poor stability. Here, at room temperature, AgI with different concentrations (5%, 10%, 20% and 30%) were coupled into Ag2CO3, producing a series of novel AgI/Ag2CO3 composite photocatalysts. The effects of AgI addition on the Ag2CO3 catalyst for photocatalytic degradation of methyl orange (MO) under visible light irradiation have been investigated. Some physicochemical technologies like N2 physical adsorption/desorption, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) were applied to characterize these products. Results show that the photocatalytic degradation activity of AgI/Ag2CO3 photocatalyst is much higher than that of pure AgI and Ag2CO3. With the optimal content of AgI (20wt%), the AgI/Ag2CO3 exhibits the highest photocatalytic degradation efficiency. Its first order reaction rate constant (0.54h−1) is 20 times of that of AgI (0.026h−1) and 3.6 times of that of Ag2CO3 (0.15h−1). The characterizations and theory calculation show that AgI and Ag2CO3 have suitably matched band gap structures. The formation of AgI/Ag2CO3 heterojunction with intimate interface could effectively increase the separation efficiency of the e−/h+ pairs and promote the production of •OH and O2•− radicals, which brings about the fast degradation rate of the dye and an increase in photocatalytic stability.
A p-type silicon nanowire array (SiNW) with a core-shell-structured Ni@In co-catalyst was fabricated for solar energy-driven reduction of CO2 and H2O into formate, an important feedstock for ...industry.
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Developing an efficient artificial photosynthetic system for transforming carbon dioxide and storing solar energy in the form of chemical bonds is one of the greatest challenges in modern chemistry. However, the limited choice of catalysts with wide light absorption range, long-term stability and excellent selectivity for CO2 reduction makes the process sluggish. Here, a core-shell-structured non-noble-metal Ni@In co-catalyst loaded p-type silicon nanowire arrays (SiNWs) for efficient CO2 reduction to formate is demonstrated. The formation rate and Faradaic efficiency of formate over the Ni@In/SiNWs catalyst reach 58 μmol h−1 cm−2 and 87% under the irradiation of one simulated sunlight (AM 1.5G, 100 mW cm−2), respectively, which are about 24 and 12 times those over the pristine SiNWs. The enhanced photoelectrocatalytic performance for CO2 reduction is attributed to the rational combination of Ni capable of effectively extracting the photogenerated electrons and In responsible for the selective activation of CO2.
Novel Nd
3+
-doped
β
-Bi
2
O
3
/Bi
2
O
2
CO
3
composite nanoplates have been synthesized via a facile phase transformation route. The products generated in the phase transformation process of Nd
3+
...-doped Bi
2
O
2
CO
3
crystals were analyzed by a series of physicochemical techniques, e.g., TG-DTG, BET, XRD, SEM, TEM, FT-IR, and UV–vis DRS. The analysis results revealed that when the calcination temperature increased to 300℃, a phase transformation occurred (Bi
2
O
2
CO
3
→ Bi
2
O
3
). However, the doping of Nd
3+
could restrain the conversion of
β
-Bi
2
O
3
to
α
-Bi
2
O
3
and promote the stability of
β
-Bi
2
O
3
crystal phase during the cooling process. The obtained Nd
3+
/
β
-Bi
2
O
3
/Bi
2
O
2
CO
3
composite nanoplates possess superior visible light photocatalytic performance in the decomposition of phenols (phenol, 2,4-dichlorophenol, bisphenol A, 4-nitrophenol) and acid orange II. The intimate
β
-Bi
2
O
3
/Bi
2
O
2
CO
3
heterojunction largely boosted the separation of photo-generated electrons and holes. Moreover, the doped Nd
3+
could also participate in the capture of electrons. Thus, more photo-generated electrons and holes are available to participate in the decomposition of pollutants.
Graphical abstract
The Nd
3+
doped
β
-Bi
2
O
3
/Bi
2
O
2
CO
3
composite nanosheets synthesized
via
a facile phase transformation route display superior visible light photocatalytic performance for phenols (phenol, 2,4-dichlorophenol, bisphenol A, 4-nitrophenol) and dye mineralization.
With the decrease of fossil resources and the large amount of CO2 emissions, research on the preparation of fuels and chemicals using CO2 has attracted wide attention. The efficient activation of ...CO2, as an extremely stable small molecule, is one of the most challenging scientific problems in chemistry. The photoelectrocatalytic reduction of CO2 is based on solar energy and water as energy and electron sources, respectively. It is an effective means to prepare renewable fuels, namely, artificial photosynthesis, which is one of the ideal ways to realize the resource utilization of CO2. The p-type silicon nanowire arrays (SiNWs) have a potential application value for photocathode materials due to their excellent performance, such as the photoelectric effect, high surface activity, high electron transport characteristics, high stability and so on. This review focuses on the design and fabrication of SiNW based photoelectrodes and their recent progress for the efficient photoelectrocatalytic reduction of CO2 to fuels and chemicals. The typical reaction modes (photocathode mode, photoanode mode and double light electrode mode) for the photoelectrocatalytic reduction of CO2 are presented and analyzed. Furthermore, the preparation methods of SiNWs, such as the laser ablation, chemical vapor deposition (CVD) and metal-assisted chemical etching method, are also discussed, especially, the metal-assisted chemical etching method. The photoelectrocatalytic activity of pure SiNWs, anchoring metal nanoparticle cocatalysts (monometal and double metal structures), anchoring metal complex cocatalysts, anchoring non-metal nanoparticle cocatalysts and combining a photoanode with photocathode, are summarized and analyzed. Future prospects will be addressed in the last part. This review aims to provide deep insights into the rational design of efficient photoelectrodes for the photoelectrocatalytic reduction of CO2 to fuels and chemicals, achieving the carbon peak and carbon neutral goals as soon as possible.
Herein, well‐crystallized ZnTiO3 particles are first prepared by hydrothermal method. A series of S‐scheme heterojunction photocatalysts of ZnTiO3/g‐C3N4 (referred to as ZTO/CN) with different mass ...ratios are synthesized by successfully doping ZnTiO3 in g‐C3N4 precursors and loading ZnTiO3 onto g‐C3N4 nanosheets by calcination. It is clearly found that the ZnTiO3 particles are successfully loaded on g‐C3N4 nanosheets by the X‐ray diffractometer, energy‐dispersive X‐ray spectra, and high‐resolution transmission electron microscopy images. Moreover, the specific surface area of 3.0% ZTO/CN is higher than that of pure g‐C3N4. Using triethanolamine as the hole sacrificial agent, the highest CO and H2 yields are achieved in the 3.0% ZTO/CN composite catalyst under the xenon lamp irradiation for 1 h. The generation rates of CO and H2 reach 15.19 and 5.77 μmol g−1 h−1, respectively, which are 2.9 and 4.1 times higher than that of pure g‐C3N4. The CO and H2 yields of the ZTO/CN composite catalyst show a trend of increasing and then decreasing with the increasing of ZnTiO3 content, which is due to the fact that excess ZnTiO3 can lead to a reduction of the effective heterojunction interface between ZnTiO3 and g‐C3N4, decreasing the transfer and separation efficiency of photogenerated electrons and holes and thus reducing the photocatalytic activity.
An ultrasonic method was developed to fabricate novel mesoporous TiO2 nanocrystals doped with a high concentration of N (N/TiO2). The nanocrystals were characterized by physicochemical methods ...including N2 physical adsorption/desorption, X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, transmission electron microscopy, and UV-Vis diffuse reflectance spectroscopy. The photocatalytic degradation of dimethyl phthalate, a hazardous chemical in water, by the prepared N/TiO2 nanocrystals under visible light irradiation (400–660 nm) was investigated. The results show that N-doping efficiency under ultrasonic irradiation is 3.2 times higher than under typical conditions, and the produced TiO2 nanocrystals have mesoporous structure. N/TiO2 fabricated under ultrasound exhibited much higher efficiency for the degradation of dimethyl phthalate than that prepared under typical conditions. The high photocatalytic degradation activity of N/TiO2 fabricated under ultrasound is mainly attributed to its high N content effectively increasing its ability to absorb visible light.
采用超声波辐射法制备了具有介孔结构的高浓度氮掺杂TiO2纳米晶(N/TiO2). 采用N2物理吸附/X射线粉末衍射/X射线光电子能谱/透射电镜/光致发光谱和紫外-可见漫反射光谱等手段对N/TiO2进行了表征. 以波长为400–660 nm的可见光为光源, 以水体污染物邻苯二甲酸二甲酯为降解对象, 考察了不同制备方法对N/TiO2光催化性能的影响. 结果表明, 超声波辐射使氮掺杂浓度提高了2.2倍, 该法制备的N/TiO2同时具有较好的介孔结构, 表现了更高的光催化降解邻苯二甲酸二甲酯的活性. 其活性提高的主要原因是N/TiO2含有更高浓度的氮和对可见光具有更强的吸收能力.
An ultrasonic method was developed to fabricate mesoporous TiO2 nanocrystals doped with high concentration of N. N doping causes strong visible light absorption and high photocatalytic activity towards degradation of dimethyl phthalate under visible light irradiation.
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