Showing papers on "Photocatalysis published in 2020"

Designing a 0D/2D S-Scheme Heterojunction over Polymeric Carbon Nitride for Visible-Light Photocatalytic Inactivation of Bacteria.

Abstract: Constructing heterojunctions between two semiconductors with matched band structure is an effective strategy to acquire high-efficiency photocatalysts. The S-scheme heterojunction system has shown great potential in facilitating separation and transfer of photogenerated carriers, as well as acquiring strong photoredox ability. Herein, a 0D/2D S-Scheme heterojunction material involving CeO2 quantum dots and polymeric carbon nitride (CeO2 /PCN) is designed and constructed by in situ wet chemistry with subsequent heat treatment. This S-scheme heterojunction material shows high-efficiency photocatalytic sterilization rate (88.1 %) towards Staphylococcus aureus (S. aureus) under visible-light irradiation (λ≥420 nm), which is 2.7 and 8.2 times that of pure CeO2 (32.2 %) and PCN (10.7 %), respectively. Strong evidence of S-scheme charge transfer path is verified by theoretical calculations, in situ irradiated X-ray photoelectron spectroscopy, and electron paramagnetic resonance.

Conjugated polymers for visible-light-driven photocatalysis

Abstract: Conjugated polymers have recently been under active investigation as promising alternatives to traditional inorganic semiconductors for photocatalysis. This is due to their unique advantages of low cost, high chemical stability, and molecularly tunable optoelectronic properties. This critical review summarizes the recent advancements in π-conjugated polymers for visible-light-driven photocatalytic applications including water splitting, CO2 reduction, organic transformation and degradation of organic dyes. Special emphasis is placed on how the changes in the polymer structure could influence their physicochemical properties and photocatalytic activities. This structure–activity relationship analysis should guide rational molecular design of conjugated polymers for improved photocatalytic activity.

Recent advances in MOF-based photocatalysis: environmental remediation under visible light

Abstract: Visible light-induced photocatalysis is a promising way for environmental remediation due to efficient utilization of solar energy. Recently, metal–organic frameworks (MOFs) have attracted increasing attention in the field of photocatalysis. In comparison with traditional metal oxide semiconductors, MOFs have many advantages, such as high specific surface area, rich topology and easily tunable porous structure. In this review, we aim to summarize and illustrate recent advances in MOF-based photocatalysis for environmental remediation under visible light, including wastewater treatment, air purification and disinfection. A series of strategies have been designed to modify and regulate pristine MOFs for enhanced photocatalytic performance, such as ligand functionalization, mixed-metal/linker strategy, metal ion/ligand immobilization, dye sensitization, metal nanoparticle loading, carbon material decoration, semiconductor coupling, MOF/COF coupling, carrier loading and magnetic recycling. The above modifications may result in extended visible light absorption, efficient generation, separation and transfer of photogenerated charges, as well as good recyclability. However, there are still many challenges and obstacles. In order to meet the requirements of using MOF photocatalysis as a friendly and stable technology for low-cost practical applications, its future development prospects are also discussed.

Noble-metal-free Ni2P modified step-scheme SnNb2O6/CdS-diethylenetriamine for photocatalytic hydrogen production under broadband light irradiation

Abstract: Step-scheme (S-scheme) photocatalytic system has been considered as an effective method for solar energy conversion by utilizing broadband solar energy, realizing easy separation of photoexcited carriers and strong redox ability. Herein, the novel ternary Ni2P cocatalysted two-dimensional (2D)/2D SnNb2O6/CdS-diethylenetriamine (SNO/CdS-D) system was designed and fabricated. The S-scheme SNO/CdS-D heterostructure gives photocatalytic hydrogen production of 7808 μmol g−1 h−1, which is about 130.13 and 2.35 times stronger than that of SNO and CdS-D. Further, noble-metal-free Ni2P cocatalyst is decorated into SNO/CdS-D heterostructure, the photocatalytic hydrogen evolution performance could be enhanced to 11,992 μmol g−1 h−1. Additionally, XPS analysis and DFT calculation revealed the carriers moves from CdS-D to SNO and then to Ni2P in the Ni2P-SNO/CdS-D nanocomposite. This work will give a reliable and clear insight into the interface and surface design of the 2D catalysts and offer a broadband photocatalytic hydrogen evolution process without noble metal cocatalysts.

1D porous tubular g-C3N4 capture black phosphorus quantum dots as 1D/0D metal-free photocatalysts for oxytetracycline hydrochloride degradation and hexavalent chromium reduction

Abstract: As an "up-and-coming" two-dimensional (2D) material, black phosphorus (BP) has attracted much attention due to its abundant metal-free properties and broad application prospects in photocatalysis. This study introduces a promising sunlight-driven metal-free photocatalyst for oxytetracycline hydrochloride degradation and hexavalent chromium reduction in water and wastewater. The roles of BP quantum dots (BPQDs) in the distribution of electrons and photocatalytic performances were well identified by experimental and density functional theory (DFT) calculations. As expected, the specially designed 0D/1D structure shows unusual photocatalytic efficiency toward the degradation of oxytetracycline hydrochloride (0.0276 min−1) and reduction of hexavalent chromium (0.0404 min−1). Reactive species, namely, O2− and h+ comprised the primary photocatalytic mechanisms for oxytetracycline hydrochloride degradation. This work highlights that the combination of tubular g-C3N4 (TCN) with BPQDs facilitates the charge spatial separation in the photocatalytic process, and provides alternative strategy for design of highly active and metal-free nanomaterials toward environmental remediation and sustainable solar-to-chemical energy conversion.

A Promoted Charge Separation/Transfer System from Cu Single Atoms and C 3 N 4 Layers for Efficient Photocatalysis

Abstract: Establishing highly effective charge transfer channels in carbon nitride (C3 N4 ) for enhancing its photocatalytic activity is still a challenging issue. Herein, for the first time, the engineering of C3 N4 layers with single-atom Cu bonded with compositional N (CuNx ) is demonstrated to address this challenge. The CuNx is formed by intercalation of chlorophyll sodium copper salt into a melamine-based supramolecular precursor followed by controlled pyrolysis. Two groups of CuNx are identified: in one group each of Cu atoms is bonded with three in-plane N atoms, while in the other group each of Cu atoms is bonded with four N atoms of two neighboring C3 N4 layers, thus forming both in-plane and interlayer charge transfer channels. Importantly, ultrafast spectroscopy has further proved that CuNx can greatly improve in-plane and interlayer separation/transfer of charge carriers and in turn boost the photocatalytic efficiency. Consequently, the catalyst exhibits a superior visible-light photocatalytic hydrogen production rate (≈212 µmol h-1 /0.02 g catalyst), 30 times higher than that of bulk C3 N4 . Moreover, it leads to an outstanding conversion rate (92.3%) and selectivity (99.9%) for the oxidation of benzene under visible light.

MIL-101(Fe)/g-C3N4 for enhanced visible-light-driven photocatalysis toward simultaneous reduction of Cr(VI) and oxidation of bisphenol A in aqueous media

Abstract: Heterostructured composites with an excellent photocatalytic activity have attracted increasing attention because of their great application in environmental remediation. Herein, a MIL-101(Fe)/g-C3N4 heterojunction was synthesized via in-situ growth of MIL-101(Fe) onto g-C3N4 surface. The heterojunctions were applied as a bifunctional photocatalyst for simultaneous reduction of Cr(VI) and degradation of bisphenol-A (BPA) under visible light and exhibited an obvious enhancement in photocatalytic performance compared with MIL-101(Fe) or g-C3N4. The improved activity could be attributed to the enhanced light absorption and efficient charge carrier separation by forming a direct Z-scheme heterojunction with appropriate band alignment between MIL-101(Fe) and g-C3N4. The radical trapping and electron spin resonance showed that photo-generated electrons are responsible for the reduction of Cr(VI) and BPA degradation, following an oxygen-induced pathway. This work provides new insight into the construction of metal-free semiconductor/MOFs heterojunctions as a bifunctional visible-light-driven photocatalyst for efficient and simultaneous treatment of multiple toxic pollutants in water.

Regulating Photocatalysis by Spin-State Manipulation of Cobalt in Covalent Organic Frameworks.

Abstract: While catalysis is highly dependent on the electronic structure of the catalyst, the understanding of catalytic performance affected by electron spin regulation remains challenging and rare. Herein, we have developed a facile strategy to the manipulation of the cobalt spin state over covalent organic frameworks (COFs), COF-367-Co, by simply changing the oxidation state of Co centered in the porphyrin. Density functional theory (DFT) calculations together with experimental results confirm that CoII and CoIII are embedded in COF-367 with S = 1/2 and 0 spin ground states, respectively. Remarkably, photocatalytic CO2 reduction results indicate that COF-367-CoIII exhibits favorable activity and significantly enhanced selectivity to HCOOH, accordingly much reduced activity and selectivity to CO and CH4, in sharp contrast to COF-367-CoII. The results highlight that the spin-state transition of cobalt greatly regulates photocatalytic performance. Theoretical calculations further disclose that the presence of CoIII in COF-367-Co is preferable to the formation of HCOOH but detrimental to its further conversion, which clearly accounts for its distinctly different photocatalysis over COF-367-CoII. To the best of our knowledge, this is the first report on regulating photocatalysis by spin state manipulation in COFs.

Surface Engineering of g-C 3 N 4 by Stacked BiOBr Sheets Rich in Oxygen Vacancies for Boosting Photocatalytic Performance

Abstract: BiOBr containing surface oxygen vacancies (OVs) was prepared by a simple solvothermal method and combined with graphitic carbon nitride (g-C3 N4 ) to construct a heterojunction for photocatalytic oxidation of nitric oxide (NO) and reduction of carbon dioxide (CO2 ). The formation of the heterojunction enhanced the transfer and separation efficiency of photogenerated carriers. Furthermore, the surface OVs sufficiently exposed catalytically active sites, and enabled capture of photoexcited electrons at the surface of the catalyst. Internal recombination of photogenerated charges was also limited, which contributed to generation of more active oxygen for NO oxidation. Heterojunction and OVs worked together to form a spatial conductive network framework, which achieved 63 % NO removal, 96 % selectivity for carbonaceous products (that is, CO and CH4 ). The stability of the catalyst was confirmed by cycling experiments and X-ray diffraction and transmission electron microscopy after NO removal.

Synthesis of Leaf‐Vein‐Like g‐C 3 N 4 with Tunable Band Structures and Charge Transfer Properties for Selective Photocatalytic H 2 O 2 Evolution

Abstract: Leaf‐vein‐like g‐C3N4 synthesized via a KBH4‐assisted thermal polycondensation strategy exhibits enhanced optical absorption, efficient charge carrier separation, and ample active sites, accordingly enabling excellent photocatalytic H2O2 evolution. The synergistic effect of B doping and defect sites on the improvement of catalyst performance is fully discussed by experiments and density functional theory calculations.

Recent advances in ozone-based advanced oxidation processes for treatment of wastewater- A review

Abstract: The wastewater reclamation is the need of today's world. Advanced oxidation processes (AOPs) are considered as a good option for removing recalcitrant organic materials in wastewater by oxidation reactions with powerful, non-selective hydroxyl radical (OH•). Ozone alone does not cause complete oxidation of some refractory organic compounds and has a low reaction rate. The ozone is combined with H2O2, UV light, catalyst, ultrasound to enhance the generation of hydroxyl radicals to increase the efficiency of the treatment process. The ozone-based AOPs have been proved to be effective in detoxifying an ample range of industrial effluents containing recalcitrant organics, pharmaceutical products, pesticides, phenols, dyes, etc. Ozone based AOP processes such as O3/UV, O3/H2O2, O3/Fe (II), O3/metal oxide catalyst, O3/activated carbon, O3/ultrasound, O3/Fenton, photocatalytic ozonation were discussed. A review of ozone-based AOP processes as a combination of ozonation with other techniques for the degradation and mineralization of recalcitrant organics present in the industrial/municipal wastewater based on the recently published work were reported.

3D hierarchical H2-reduced Mn-doped CeO2 microflowers assembled from nanotubes as a high-performance Fenton-like photocatalyst for tetracycline antibiotics degradation

Abstract: Developing of active and synergistic system is fundamentally important to rapidly and efficiently remove persistent toxic and hazardous pollutants. Herein, we report a coupling system by integrating sulfate radical-based Fenton-like process with visible light-driven photocatalysis for fast removal of three typical tetracycline antibiotics in water, i.e., tetracycline (TC), chlortetracycline (CTC), and oxytetracycline (OTC), where the newly-designed nanotubes-assembled 3D hierarchical H2-reduced Mn-doped CeO2 microflowers (re-Mn-CeO2 NMs) are developed as efficient Fenton-like photocatalyst for peroxymonosulfate (PMS) activation. The obtained re-Mn-CeO2 NMs samples, featuring large surface area, good visible light response, excellent redox properties, and abundant oxygen vacancy, exhibit appreciable adsorption capacity, remarkable catalytic performance, and favorable stability. Especially, in the optimal reaction system (re-7Mn-CeO2 NMs/PMS/Vis), the degradation efficiencies of TC, CTC, and OTC reach up to 98.6%, 97.4%, and 88.1% only in 10 min of irradiation. All residues can be completely eliminated in 60 min, which is ∼1.1 and 2.0-fold higher than those of Fenton-like reaction and photocatalysis alone, confirming the synergistic effect of Fenton-like process and photocatalysis occurred in the coupling system. Moreover, the possible decomposition pathways, main reactive oxygen species, and reasonable enhanced mechanism for the Fenton-like photocatalytic system are systematically investigated. Our findings highlight that the Fenton-photocatalysis synergy holds great promising for environment remediation, and offer a feasible means to tune the performance of CeO2-based materials especially in Fenton-like photocatalytic oxidation of antibiotics.

Rare-Earth Single-Atom La-N Charge-Transfer Bridge on Carbon Nitride for Highly Efficient and Selective Photocatalytic CO2 Reduction.

Abstract: Photocatalytic CO2 conversion into valuable solar fuels is highly appealing, but lack of directional charge-transfer channel and insufficient active sites resulted in limited CO2 reduction efficiency and selectivity for most photocatalytic systems. Herein, we designed and fabricated rare-earth La single-atoms on carbon nitride with La-N charge-transfer bridge as the active center for photocatalytic CO2 reaction. The formation of La single-atoms was certified by spherical aberration-corrected HAADF-STEM, STEM-EELS, EXAFS, and theoretical calculations. The electronic structure of the La-N bridge enables a high CO-yielding rate of 92 μmol·g-1·h-1 and CO selectivity of 80.3%, which is superior to most g-C3N4-based photocatalytic CO2 reductions. The CO production rate remained nearly constant under light irradiation for five cycles of 20 h, indicating its stability. The closely combined experimental and DFT calculations clearly elucidated that the variety of electronic states induced by 4f and 5d orbitals of the La single atom and the p-d orbital hybridization of La-N atoms enabled the formation of charge-transfer channel. The La-N charge bridges are found to function as the key active center for CO2 activation, rapid COOH* formation, and CO desorption. The present work would provide a mechanistic understanding into the utilization of rare-earth single-atoms in photocatalysis for solar energy conversion.

In situ preparation of g-C3N4/Bi4O5I2 complex and its elevated photoactivity in Methyl Orange degradation under visible light.

Abstract: A graphite carbon nitride (g-C3N4) modified Bi4O5I2 composite was successfully prepared in-situ via the thermal treatment of a g-C3N4/BiOI precursor at 400°C for 3 hr. The as-prepared g-C3N4/Bi4O5I2 showed high photocatalytic performance in Methyl Orange (MO) degradation under visible light. The best sample presented a degradation rate of 0.164 min−1, which is 3.2 and 82 times as high as that of Bi4O5I2 and g-C3N4, respectively. The g-C3N4/Bi4O5I2 was characterized by X-ray powder diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectra (DRS), electrochemical impedance spectroscopy (EIS) and transient photocurrent response in order to explain the enhanced photoactivity. Results indicated that the decoration with a small amount of g-C3N4 influenced the specific surface area only slightly. Nevertheless, the capability for absorbing visible light was improved measurably, which was beneficial to the MO degradation. On top of that, a strong interaction between g-C3N4 and Bi4O5I2 was detected. This interplay promoted the formation of a favorable heterojunction structure and thereby enhanced the charge separation. Thus, the g-C3N4/Bi4O5I2 composite presented greater charge separation efficiency and much better photocatalytic performance than Bi4O5I2. Additionally, g-C3N4/Bi4O5I2 also presented high stability. •O2− and holes were verified to be the main reactive species.

Boosting the activity and stability of Ag-Cu2O/ZnO nanorods for photocatalytic CO2 reduction

Abstract: To construct semiconductor-based photocatalysts for carbon dioxide (CO2) reduction with high activity and stability remains a long-term goal. Herein, we report a ternary Ag-Cu2O/ZnO nanorods (NRs) hybrid catalyst with efficient charge carrier separation/transfer and CO2 adsorption capacity, which demonstrates much improved activity in comparison with bare ZnO NRs for photocatalytic CO2 reduction to carbon monoxide (CO) under UV–vis light. Mechanistic studies reveal that the deposited Cu2O enhances the CO2 chemisorption on the surface of catalysts and the formation of Z-scheme system between Cu2O and ZnO facilitates the photogenerated charge separation. The subsequent assembly of Ag nanoparticles (NPs) onto Cu2O is able to further promote the transfer of electrons due to the “electron sink” effect of Ag, which leads to the higher photocatalytic activity. As such, the synergy effect of strong CO2 chemisorption and multiple electrons transfer results in the boosted photocatalytic activity of Ag-Cu2O/ZnO NRs for CO2 reduction. In addition, compared with the binary Cu2O/ZnO NRs, the activity of Ag-Cu2O/ZnO NRs can be well maintained after multiple-cycle reaction. The possible reason is that the deposited Ag can alleviate the self-photoreduction of Cu2O by transferring the excess electrons accumulated in the conduction band (CB) of Cu2O, thus preserving the stability of the Ag-Cu2O/ZnO NRs photocatalyst.