Sunlight-driven photocatalysis has emerged as a potential technology to address organic pollutant issues. Here, we report the first Rh-doped hollow-structured TiO2 photocatalyst, which is highly active in the photocatalytic decomposition of organic pollutants under solar light. We achieved this by introducing Sr2+ as a co-doping agent, which stabilized the hollow structure at high temperatures and enabled us to control the oxidation state of Rh. The designed photocatalyst exhibited strong visible light absorption (up to 600 nm), and a very high surface area (up to 140 m2 g−1). As a result, the Sr/Rh-doped TiO2 hollow photocatalysts demonstrated a photocatalytic efficiency (PE) of 0.242%, which was at least 8 times higher than that of commercial TiO2 (0.03%) and 25 times higher than that of bulk Sr/Rh–TiO2 (0.01%), in the photocatalytic decomposition of isopropanol under solar light irradiation.
A critical drawback of existing materials, which restricts the photocatalytic efficiency, is the fast recombination of charge carriers. To address this challenge, loading reduction and oxidation co‐catalysts on two opposite surfaces of a hollow semiconductor is a critical approach to improve the photocatalytic performance. These co‐catalysts mainly act as oxidation and reduction active sites, while suppressing the charge recombination. Moreover, the development of a novel and efficient co‐catalyst that boosts charge separation is a very important feature for the photocatalytic performance. Herein, we report the first synthesis of hollow Pt/TiO2/CxNy‐triazine nanocomposite using carbon colloidal spheres as a hard template, in which Pt and CxNy‐triazine are located on the two opposite hollow surfaces. CxNy‐based triazine species formed from cyanamide during calcination do not only stabilize the hollow structure and significantly enhance the surface area of Pt/TiO2/CxNy‐triazine, but also act as an efficient oxidation co‐catalysts. This new type of nanocomposite exhibits one of the best TiO2‐based photocatalysts working under solar light irradiation to date. It is 125 and 62 times higher than that of Pt/TiO2–P25 for hydrogen generation and methanol decomposition, respectively.
3D architectures porous epsilon-type manganese dioxide (ε-MnO2) microcubes (PEMD) are successfully prepared by a glucose-urea-assisted hydrothermal synthesis of MnCO3-carbon composites followed by annealing. It turns out that urea essentially assists in building the cubic shape while glucose plays a crucial role to form carbon inside the microcrystals, which are latterly removed by annealing to generate the porous structure. As a result, ε-MnO2 materials possessing extraordinary features including the high porosity, reducibility, lattice oxygen reactivity and Mn4+ fraction, are feasible tailored. These unique properties, all together, significantly improve the catalytic performances of complete oxidation of toluene. Thus, it is found that the optimal catalyst (manganese-glucose-urea ratio of 6-2-6) synthesized at 180 °C exhibits an excellent activity for the complete oxidation of toluene (T90 = 243 °C, lower 10 °C than that of pristine ε-MnO2) and stability up to 10 h.
The photoassisted catalytic reaction, conventionally known as photocatalysis, is expanding into the field of energy and environmental applications. It is widely known that the discovery of TiO2‐assisted photochemical reactions has led to several unique applications, such as degradation of pollutants in water and air, hydrogen production through water splitting, fuel conversion, cancer treatment, antibacterial activity, self‐cleaning glasses, and concrete. These multifaceted applications of this phenomenon can be enriched and expanded further if this process is equipped with more tools and functions. The term “photoassisted” catalytic reactions clearly emphasizes that photons are required to activate the catalyst; this can be transcended even into the dark if electrons are stored in the material for the later use to continue the catalytic reactions in the absence of light. This can be achieved by equipping the photocatalyst with an electron‐storage material to overcome current limitations in photoassisted catalytic reactions. In this context, this article sheds lights on the materials and mechanisms of photocatalytic reactions under light and dark conditions. The manifestation of such systems could be an unparalleled technology in the near future that could influence all spheres of the catalytic sciences.
This work reports on the fabrication of Fe2O3/Pt/Au nanocomposite immobilized on g-C3N4 surface with highly enhanced visible light photocatalytic activity toward efficient and stable hydrogen production. The results showed that the designed nanosystem photocatalysts were successfully fabricated, with intimate interfacial contact between g-C3N4 and Fe2O3 and uniform distribution of Pt and Au on the surface of g-C3N4 which can significantly improve the photocatalytic activity compared to its constituents. Localized surface plasmon resonance of Au, Z-scheme heterojunction interaction of two semiconductors, Schottky barriers and active sites of Pt can effectively promote hydrogen production. The photocatalytic mechanism of the produced system is suggested. The H2-evolution rate of 4.6 μmol h−1 mg−1 was achieved and the synthesized samples exhibited good photocatalytic stability in recycling H2 evolution. This work provides a new way to design effective photocatalysts for splitting water under solar light, which can simultaneously extend light absorption range for better electron-hole generation, reduce carrier recombination and increase H+ absorption for efficient H2 production.
The development of efficient photocatalysts that can work both under visible light and in darkness remains an important research target for environmental applications. A large number of photocatalysts have been reported, but they still suffer from low activity that originates from fundamental efficiency bottlenecks: i.e., weak photon absorption and poor electron–hole pair separation when operating under irradiation, and poor electron storage capacity when operating in darkness. Herein, we report the first synthesis of hollow double-shell H:Pt–WO3/TiO2–Au nanospheres with high specific surface area, large TiO2/WO3 interfacial contact and strong visible light absorption. Because of these features, this type of nanocomposite shows high charge separation and electron storage capacity, and exhibits efficient degradation of organic pollutants both under visible light (λ ≥ 420 nm) and in darkness. In addition, CO2 generation from formaldehyde gave a high quantum efficiency of 77.6%.
Nickel deposited S-doped carbon nitride (Ni–S:g-C3N4/Ni-SCN) nanosheets have been synthesized using calcination followed by a sulfidation process. X-ray photoelectron spectra revealed that the doped S atoms are successfully introduced into the 301 lattices of the host g-C3N4. XPS spectra indicated that the deposited Ni species are chemically bonded onto the host SCN nanosheets through sulfur bonds. The sunlight-driven photocatalytic hydrogen production efficiency of the synthesized Ni-SCN nanosheets is found to be 3628 μmol g–1 h–1, which is around 1.5 folds higher than that of Pt-SCN that synthesized in the present study. The observed efficiency is attributed to the chemical bonding of Ni through S that largely favored the photocatalytic process in terms of charge-separation as well as self-catalytic reactions. The apparent quantum efficiency of the photocatalyst at 420 nm is estimated to be 17.2%, which is relatively one of the higher values reported in the literature. The photocatalytic recyclability results showed consistent hydrogen evolution efficiency over 4 cycles (8 h) that revealed the excellent stability of the photocatalyst. This work has demonstrated that the chemical bonding of cocatalyst onto the host photocatalyst is relatively an effective strategy as compared to the conventional deposition of cocatalyst by means of electrostatic or van der Waals forces.
Herein, we report a novel air-assisted carbon sphere combustion process to produce phase-tunable anatase-rutile (A/R) C/Pt-TiO2 photocatalysts for hydrogen generation and organic pollutant degradation under solar light irradiation. In the formed carbon/amorphous TiO2 core/shell structure, the carbon-core was acted as a fuel to prepare the mixed phase A/R TiO2 nanostructures. The A/R ratio of the TiO2 nanoparticles was tuned by varying the purged air flow during the combustion process. The obtained materials exhibited several unique properties not achievable using conventional methods, including anatase/rutile homojunction, co-existence of C and Pt/PtO and very high surface area, significantly improved charge separation and transfer characteristics towards excellent photocatalytic properties. Eventually, the photocatalytic activities of the obtained materials were found to be more than 23 and 17 folds higher than commercial TiO2-P25 for hydrogen generation and organic pollutant degradation, respectively.
Abstract This study aimed at providing a route towards the production of a novel exopolysaccharide (EPS) from fermented bamboo shoot-isolated Lactobacillus fermentum. A lactic acid bacteria strain, with high EPS production ability, was isolated from fermented bamboo shoots. This strain, R-49757, was identified in the BCCM/LMG Bacteria Collection, Ghent University, Belgium by the phenylalanyl-tRNA synthetase gene sequencing method, and it was named Lb. fermentum MC3. The molecular mass of the EPS measured via gel permeation chromatography was found to be 9.85 × 104 Da. Moreover, the monosaccharide composition in the EPS was analyzed by gas chromatography–mass spectrometry. Consequently, the EPS was discovered to be a heteropolysaccharide with the appearance of two main sugars—D-glucose and D-mannose—in the backbone. The results of one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance spectroscopy analyses prove the repeating unit of this polysaccharide to be [→6)-β-D-Glcp-(1→3)-β-D-Manp-(1→6)-β-D-Glcp-(1→]n, which appears to be a new EPS. The obtained results open up an avenue for the production of novel EPSs for biomedical applications.
Abstract Photocatalysts comprising 2D carbon nitride-based systems have emerged as a fervently researched topic for addressing the problems of fuel depletion and the environment. However, the photocatalytic activities of pristine g-C3N4 are still mediocre and suffer from issues pertaining to the restrictions in light absorption, charge separation, and carrier-induced surface reactions; however, efforts have been made in the past decades to boost the efficiencies. This review endeavors to present a roadmap to prepare high-performance g-C3N4 photocatalysts by expounding the cutting-edge research on g-C3N4 materials either as a single component or g-C3N4-based composites including current challenges and perspectives on this topical theme. We believe that this review will provide a broader picture and recommendations for the preparation of superior g-C3N4 photocatalysts towards a greener, cleaner, and resilient future.
Abstract Two-dimensional MXenes have gained tremendous interest as frontier materials for a wide variety of applications and play a pivotal role in the development of future energy, electronic and optoelectronic devices as they exhibit high catalytic activity in diverse electrocatalytic and photocatalytic devices. The fabrication and application of MXenes as catalysts have become more progressive in recent years and more than 30 different varieties have been experimentally discovered and utilized. In this review, we rationally summarized and discussed the most recent advances in the synthesis and specific applications of MXenes as electrocatalysts and photocatalyst for hydrogen evolution reaction (HER) and CO2 reduction reaction (CO2RR) including strategies for boosting their catalytic activity for target products. Finally, we highlight the lingering challenges and direction for the future development of MXenes as catalysts for HER and CO2RR.
Converting solar energy into fuel via photo-assisted water splitting to generate H2 or drive CO2 photoreduction is an attractive scientific and technological goal to address the increasing global demand for energy and to reduce the impact of energy production on climate change. Solar-driven hydrogenation of CO2 into value-added chemical products is one of the most promising strategies for reducing CO2 and is anticipated to be a sustainable energy source shortly. In this study, we focus on the utilization of different sustainable H2 sources for the photoreduction of CO2 to value-added organic products. Various photocatalysts, photoreactor configurations, and reaction parameters for the photoreduction of CO2 are discussed. For future research endeavors, a general approach for the photoreduction of CO2 to mimic natural photosynthesis, in which the H2 source is provided directly during the photocatalytic water splitting, is proposed and verified to generate value-added organic products successfully.
Graphitic carbon nitride (g-C3N4) has emerged as promising metal-free semiconductorbased photocatalysts for solar energy conversion. However, the photocatalytic performance of gC3N4 is still moderate, due to the lack of the architecture design, which enables solar light harvesting, excited electron-hole separation as well as extending their availability for redox reactions, and far from practical application. Herein, we engineer the structure of g-C3N4 through a polyethyleneimine (PEI)/alkaline co-assisted technique. The resulting materials show the high concentration of both N3C nitrogen vacancies and hydroxyl groups on the g-C3N4 surface. These features significantly contribute to enhancing electron-hole generation and separation and harvest solar light absorption, which boosts the photocatalytic hydrogen production compared to bare gC3N4 under solar irradiation. Keywords: Photocatalysis; g-C3N4; hydrogen production; N3C nitrogen vacancies; hydroxyl groups; solar light absorption
We have demonstrated the crucial role of nitrogen vacancies toward the enhancement of the plasmonic properties of Au/g-C3N4 nanocomposites, which were prepared via the alkali-assisted synthesis and postcalcination pathway, for the effective production of hydrogen through a photocatalytic process under simulated solar light. The resulting material consisted of the nitrogen defective crumpled nanolayers of gC3N4 with strongly integrated Au plasmonic nanoparticles. It is realized from the studies that the nitrogen vacancies facilitate a stronger interaction with Au NPs and create the coexistence of the states of Au and Au(δ−) , which is eventually found to be the origin of the observed enhanced plasmonic properties of the nanocomposite. Such features have not been observed in any other conventional methods for the preparation of Au/g-C3N4, where it significantly improved (i) the light utilization abilities of the materials and (ii) electron−hole generation and separation, which collectively led to the boosting of the photocatalytic performance toward hydrogen production under simulated solar light.
The over-exploitation of fossil fuels means that research into alternative sustainable energy sources is crucial for the scientific community. The harvesting of solar energy via photocatalysis is a key approach to developing these alternatives. Furthermore, photocatalytic materials show great promise for degradation of pollutants. However, limitations in incident light utilization and charge separation are major drawbacks that restrict the activity of current artificial photosystems. Construction of hollow nano-sized photocatalysts is emerging as a promising approach to fabricating novel and effective materials, as hollow photocatalysts possess unique properties that may be exploited to overcome these challenges. This review gives a concise overview of the advantages of hollow structures for this purpose, the methodology used to prepare hollow photocatalysts, and the current state-of-the-art in the development of hollow structure photocatalysts for energy production and environmental applications