Mechanism Of Photocatalytic Reduction Research Articles

Mesoporous sulfur-doped g-C3N4@attapulgite composite as an advanced photocatalyst for efficiently uranium(VI) recovery from aqueous solutions

Photocatalytic reduction of uranium(VI) via g-C3N4 is a promising and efficient method for the recovery of radioactive uranium contamination from wastewater. In this work, the mesoporous sulfur-doped g-C3N4@attapulgite composite was first synthesized via a two-step hydrothermal-roasting method with (NH4)2S2O8 as the sulfur source and attapulgite as the supporter, respectively. As expected, the recovery efficiency of uranium(VI) using S-doped g-C3N4 was 1.80 times higher than that of g-C3N4. Additionally, compared to S-doped g-C3N4, the mesoporous S-doped g-C3N4@attapulgite composite exhibited further improved photocatalytic efficiency and stability. The experimental results further showed the uranium(VI) was quickly eliminated within 20 min by mesoporous S-doped g-C3N4@attapulgite, and the recovery rate of which remained at 88.4 % even after seven cycles. According to the XPS results and trapping experiments, the excellent uranium(VI) recovery and stability can be attributed to the adsorption capacity of attapulgite and the e- reduction from sulfur doping g-C3N4, respectively. This result contributes to understanding the enhanced photocatalytic reduction mechanism of uranium(VI) and to achieving the high-efficiency recovery of uranium from wastewater using the mesoporous S-doped g-C3N4@attapulgite composite.

Synthesis of interfacial electric field-enhanced CdS/CdxZn1-xS/ZnO ternary heterojunction by lye dissolution etching mechanism for photocatalytic H2 production and CO2 reduction

The difficulty in fabricating a multifaceted composite heterojunction system based on CdxZn1-xS limits the enhancement of photocatalytic performance. In the present scrutiny, novel ZnO/CdxZn1-xS/CdS composite heterojunctions are successfully prepared by the alkaline dissolution etching method. The internal electric field at the interface of I-type and Z-scheme heterojunction improved the effective charge separation. The ZC 8 sample exhibits excellent photocatalytic performance and the H2 production efficiency is 15.67 mmol g−1 h−1 with good stability up to 82.9% in 24-hour cycles. The performance of CH4 and CO capacity in the CO2RR process is 3.47 μmol g−1 h−1 and 23.5 μmol g−1 h−1, respectively. The photogenerated accelerated charge transport is then examined in detail by in situ X-ray photoelectron spectroscopy (ISXPS) and density functional theory (DFT) calculations. This work presents a new idea for the synthesis of CdxZn1-xS solid-solution-based materials and provides a solid reference for the detailed mechanism regarding the electric field at the heterojunction interface.

A covalent organic framework integrating photocatalytic center and electron reservoir for photocatalytic CO2 reduction to HCOOH

Direct and efficient photocatalytic conversion of CO2 into fuels and high value-added chemicals under sunlight is of great significance in alleviating the energy crisis and environmental issues. Covalent organic frameworks (COFs) have attracted much attention in the photocatalytic field as materials that can be pre-designed on demand. Taking advantage of the pre-designable properties of COFs materials, the integration of organic building blocks with photocatalytic activity and photoelectron-resident properties into frameworks can improve the electron-hole separation efficiency and photocatalytic performance. Here, we report a newly designed COF (COF-TVBT-N) with triazine and alkenyl groups that can be used as a photocatalyst to accomplish the photoreduction of CO2 to HCOOH under simulated sunlight without the assistance of metal sites and photosensitizers. Furthermore, we unambiguously reveal that the photocatalytic active center in COF-TVBT-N is TVBT through the combination of experiments and theoretical calculations. DFT calculations suggest that the adsorption of H near the active center is beneficial for the adsorption and photoreduction of CO2 in this photocatalytic system. The photoexcitation process and photocatalytic CO2 reduction mechanism of COF-TVBT-N are also reasonably deduced based on DFT calculations. This work provides ideas for the design of COFs as photocatalysts for CO2 reduction and gives insights into the mechanism of CO2 conversion to HCOOH.

Self-nitrogen-doped hierarchical porous carbon spheres as metal-free catalyst for efficient photocatalytic CO2 reduction

It is rather important to develop an efficient, stable and economical photocatalyst for solar-driven CO2 reduction. Herein, N-doped hierarchical porous carbon spheres (NPCS-F6) with metal-like activity is synthesized using acrylamide and F127 as nitrogen source and soft template, and the effective synergy between nitrogen-containing species and hierarchical pore structure makes the samples exhibit excellent CO2 reduction properties. XPS characterization illustrates that the introduced pyridine nitrogen and pyrrole nitrogen groups contribute to the increase of CO2 reduction sites on the surface of the material. N2 adsorption analysis verifies the existence of hierarchical pore structures in which micropores facilitate the exposure of more adsorption active sites, while mesopores and macropores can be used as transfer channels to connect the internal micropores and reduce the molecular diffusion resistance to improve CO2 adsorption performance. In addition, the pore structure of the samples prepared with P123 and CTAB as templates is mainly microporous, whereas carbon spheres with hierarchical pores coexisting are obtained with F127 as template. The evaluation of photocatalytic CO2 reduction activity shows that the CO yield of NPCS-F6 could reach 17.56 μmol·g−1 for 8 h, which is 1.17 times, 1.08 times and 1.07 times of the original NCS-8 (15.05 μmol·g−1), NPCS-P6 (P123 as soft template, 16.25 μmol·g−1) and NPCS-C1 (CATB as soft template, 16.39 μmol·g−1), respectively. Comprehensive characterization results are analyzed to propose a possible mechanism for photocatalytic CO2 reduction, in which photogenerated electron-hole pairs are generated inside the material under light conditions, and the photogenerated electrons are transferred to the N-6/N-5 active sites through the electron transfer channel N-Q to react with CO2 molecules adsorbed on the surface to be reduced to CO. Finally, our results provide a favorable and feasible strategy to synthesize metal-free photocatalysts for high-efficiency CO2 adsorption and targeted reduction of CO2 to CO.

Synthesis of isotype heterojunction by series calcination of multicomponent for high efficiency photocatalytic reduction of uranium

Photocatalytic reduction of soluble U(VI) to insoluble U(IV) is considered to be one of the most effective strategies for uranium contaminant removal. Graphite carbon nitride (g-C3N4) was widely used in the photocatalytic reduction of uranium due to its adjustable band structure and excellent chemical stability. Herein, through supramolecular self-assembly method, using thiourea as precursors, a carbon nitride photocatalyst (sp-ICN) with an isotype heterojunction structure was prepared by multicomponent series calcination for photocatalytic reduction of U(VI). The effects of pH, photocatalyst dosage and initial uranium concentration were examined on the effectiveness of the sp–ICN–1.0 photocatalytic reduction of uranium. The optimal reaction rate of sp–ICN–1.0 was 0.088 min−1, being 2.8 and 2.6 times that for pristine TCN (0.031 min−1) and sp-MCN (0.034 min−1), respectively. After 5 recycling experiments, more than 90% of U(VI) can still be reduced, indicating that sp–ICN–1.0 has good stability and repeatability in photocatalytic reduction of uranium. The electrochemical characterization of sp–ICN–1.0 showed that the formation of carbon nitride isotype heterojunction could improve the efficiency of photogenerated carrier separation and transfer, also reduce the resistivity of electron migration. A potential mechanism for photocatalytic reduction in U(VI) has been proposed. The result provides an idea for the further development of a novel semiconductor carbon nitride photocatalyst for the photocatalytic reduction of uranium.

Defect and nanostructure engineering of polymeric carbon nitride for visible-light-driven CO2 reduction

Sunlight-induced photocatalytic carbon dioxide (CO2) reduction to energy-rich chemicals by metal-free polymeric carbon nitride (CN) semiconductor is a promising tactic for sustained solar fuel production. However, the reaction efficiency of CO2 photoreduction is restrained seriously by the rapid recombination of photogenerated carriers on CN polymer. Herein, we incorporate the 2-aminopyridine molecule with strong electron-withdrawing group into the skeleton edge of CN layers through a facile one-pot thermal polymerization strategy using urea as the precursor, which renders the modified carbon nitride (ACN) with extended optical harvesting, abundant nitrogen defects and ultrathin nanosheet structure. Consequently, the ACN photocatalyst with desirable structural features attains enhanced separation and migration of photoexcited charge carriers. Under visible light irradiation with Co(bpy)32+ as a cocatalyst, the optimized ACN sample manifests a high CO2 deoxygnative reduction activity and high stability, providing a CO yielding rate of 17 μmol h−1, which is significantly higher than that of pristine CN. The key intermediates engaged in CO2 photoreduction reaction are determined by the in situ diffuse reflectance infrared Fourier transform spectroscopy, which sponsors the construction of the possible photocatalytic CO2 reduction mechanism on ACN nanosheets.

Mechanism of photocatalytic CO2 reduction to HCO2H by a robust multifunctional iridium complex.

The tetradentate PNNP-type IrIII complex Mes-IrPCY2 ([Cl-IrIII-H]+) is reported to be an efficient catalyst for the reduction of CO2 to formate with excellent selectivity under visible light irradiation. Density functional calculations have been carried out to elucidate the mechanism and the origin of selectivity in the present work. Calculations suggest that the double-reduced complex 1-H (1[IrI-H]0) demonstrates higher activity than the single-reduced complex 2-H (2[IrIII(L˙-)-H]+), possibly owing to the higher hydride donor ability of the former compared to the latter; thus 1-H functions as the active species in the overall CO2 reduction reaction. In the HCOO- formation pathway, the hydride of 1-H performs a nucleophilic attack on CO2via an outer-sphere fashion to generate species 1-OCHO (1[IrI-OCHO]0), which then releases HCOO- to produce an IrI intermediate. A subsequent protonation and chloride coordination of the Ir center leads to the regeneration of catalyst 1[Cl-IrIII-H]+. For the CO production, a nucleophilic attack on CO2 takes place by the Ir atom of 1-Hvia an inner-sphere manner to afford complex O2C-3-H (1[O2C-IrIII-H]0), followed by a two-proton-one-electron reduction to furnish the OC-2-H complex (2[OC-IrIII(L˙-)-H]+) after liberating a H2O. Ultimately, CO is released to form 2-H. The stronger nucleophilicity as well as smaller steric hindrance of the hydride than the Ir atom of the active species 1-H (1[IrI-H]0) is found to account for the favoring of formate formation over CO formation. Meanwhile, the CO2 reduction reaction is calculated to be preferred over the hydrogen evolution reaction, and this is consistent with the experimental product distributions.

Overall reaction mechanism of photocatalytic CO2 reduction on a Re(i)-complex catalyst unit of a Ru(ii)–Re(i) supramolecular photocatalyst

The whole mechanism of photocatalytic CO2 reduction to CO by a Ru(ii)–Re(i) supramolecular photocatalyst was successfully clarified using time-resolved infrared spectroscopy, UHPLC analysis, electrochemical measurements, and DFT calculations.

Enhanced photoreduction efficiency of Cr(VI) driven by visible light in a new Zr-based metal-organic framework modified by hydroxyl groups.

While metal-organic framework (MOF) photocatalysts have demonstrated a unique Cr(VI) photoreduction capability in recent decades, their performance is still insufficient for practical applications because of their low Cr(VI) uptake and poor visible light response. To cope with these drawbacks, a new OH-modified Zr-based MOF, termed HCMUE-1, was successfully prepared via a solvothermal method in this work. The complete characterization of HCMUE-1 was performed through various techniques, including powder X-ray diffraction (PXRD), Raman spectroscopy, Fourier transform infrared (FT-IR), thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), scanning electron microscopy combined with energy-dispersive X-ray (SEM-EDX), and X-ray photoelectron spectroscopy (XPS). The obtained data exhibited the excellent Cr(VI) photoreduction efficiency of HCMUE-1, reaching up to 98% after 90 min and almost 100% after 120 min under visible light illumination in a low acidic medium. Noteworthily, HCMUE-1 retained the same Cr(VI) removal rate for at least seven cycles without considerable loss. Further experimental investigations demonstrated that the structural stability and surface morphology of HCMUE-1 were retained after photoreduction. Moreover, the photocatalytic reduction mechanism of Cr(VI) to Cr(III) was interpreted through a series of systematic experimental measurements. These results indicate that HCMUE-1 possesses potential as an efficient photocatalyst for reducing toxic Cr(VI) species from wastewater in real-life conditions.

Localized surface plasmon resonance effect of bismuth nanoparticles in Bi/TiO2 catalysts for boosting visible light-driven CO2 reduction to CH4

Herein, the photocatalysts of metallic Bi-modified TiO2 microsphere (namely BTO) were synthesized by one-pot solvothermal method. The localized surface plasmon resonance (LSPR) effect of introduced metallic Bi nanoparticles is beneficial to improve the absorption efficiency for visible light, and its surface hot electrons can donate to the valence band of TiO2 for boosting the separation efficiency of light generated electron-hole pairs. BTO catalysts exhibit the super catalytic activity for visible light-driven CO2 reduction with H2O to CH4. The formation amount and selectivity of CH4 product over BTO-2 catalyst are 49.12 μmol g−1 and 85.48 % for 4 h, respectively. Based on the results of in-situ DRIFTS and density functional theory calculation, the mechanism for photocatalytic CO2 reduction is proposed: the visible light-driven LSPR effect on BTO catalyst can boost the key step of CO2* -to-HCO* for promoting selective generation of CH4 product. It inspires the design of efficient photocatalysts for CO2 conversion.

Atomic-level surface modification of ultrathin Bi2WO6 nanosheets for boosting photocatalytic CO2 reduction

Creating useful chemicals based on artificial CO2 photoreduction is considered to be an attractive approach to address the environmental and energy crises. Currently, its selectivity with high conversion efficiency is still a grand challenge. Here, we report the refined substitution of Bi3+ with Ag+ in ultrathin Bi2WO6 nanosheets through a liquid-phase cation exchange process, favoring a high selectivity towards the photocatalytic production of CO from CO2. The incorporation of Ag+ could not only significantly promote the adsorption of both CO2 and H2O molecules, but also facilitate the transfer of photogenerated carriers. The as-fabricated photocatalyst achieves a high CO generation rate of 116.96 μmol g−1 with a superb selectivity of 95.7 % after 6 h reaction without any sacrificial agent, approximate 4.2 times higher than that of pure Bi2WO6. The mechanism for photocatalytic CO2 reduction is proposed, based on in-situ Fourier Transform Infrared spectrometry analyses and Density Functional Theory calculations.

One-pot hydrothermal preparation of Ni and I co-doped brookite-anatase TiO2 nanoparticles with remarkably enhanced photoreduction activity of CO2 to CH4

Ni and I co-doped TiO2 nanoparticles with mixed anatase-brookite phase (Ni/I-TiO2) were synthesized by the hydrothermal-calcination method for photocatalytic CO2 reduction with H2O vapor. The I and Ni co-doping, anatase-brookite phase junction, as well as the presence of Ti(III) and Ni(III) endowed the catalyst with promoted visible light absorption, increased reduction ability of photogenerated electrons, facilitated charge separation and migration along with modulated CO2 adsorption mode and capacity, ultimately resulting in boosted photocatalytic activity and product selectivity as compared with those of pure TiO2. The CO, CH4 and O2 yields of the optimized Ni/I-TiO2 reached 3.49, 158.25 and 246.30 μmol/gcat after 15 h of light illumination, which decreased slightly after 9 cycles, and the product selectivity was above 98 % for photocatalytic reduction of CO2 to CH4 with Ni and I co-doping. The in-situ FTIR results with the observation of CH3O and CH3 intermediates confirmed CH4 formation, and the possible mechanism of photocatalytic CO2 reduction over Ni/I-TiO2 was elucidated. This work provides new insights to pursue efficient catalysts for the selective photocatalytic CO2 reduction to CH4.

Indirect Z‐scheme TiO2/BC/g‐C3N4 for efficient photocatalytic reduction of Cr(VI) in aqueous solution

AbstractBACKGROUNDThere is increasing concern regarding the rising issue of Cr(VI) pollution in aqueous solutions. It is crucial to find an effective technology for the removal of Cr(VI) in aqueous solutions. In this work, a novel TiO2/BC/g‐C3N4 heterostructure photocatalyst was successfully prepared by a simple hydrothermal method and characterized by scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, Brunauer–Emmett–Teller analysis, Fourier transform infrared spectroscopy, photoluminescence, ultraviolet–visible diffuse reflectance spectroscopy and X‐ray photoelectron spectroscopy. The photocatalytic reduction behavior of Cr(VI) on the TiO2/BC/g‐C3N4 heterostructure was investigated under visible light irradiation, and the possible mechanism of photocatalytic reduction of Cr(VI) was elucidated.RESULTSThe TiO2/BC/g‐C3N4 heterostructure photocatalyst exhibited better photoreduction activity for Cr(VI) under visible light irradiation. After 100 min irradiation with visible light, the TiO2/BC/g‐C3N4 photocatalyst achieved a removal efficiency of 89% for Cr(VI). Compared with TiO2, TiO2/BC and TiO2/g‐C3N4, the photocatalytic removal efficiency of Cr(VI) on the TiO2/BC/g‐C3N4 increased by 40%, 20% and 10% respectively. The photocatalytic reduction of Cr(VI) was dependent on the initial concentration of Cr(VI), catalyst dosage, pH value and atmosphere. Moreover, TiO2/BC/g‐C3N4 presented excellent stability and reusability after five cycles.CONCLUSIONThe TiO2/BC/g‐C3N4 heterojunction enables highly efficient photocatalytic reduction of Cr(VI) under visible light irradiation. This enhancement is primarily attributed to the construction of an indirect Z‐scheme TiO2/BC/g‐C3N4 heterojunction, which significantly improves the separation efficiency of photo‐ generated charge carriers during the photochemical process. Furthermore, the presence of BC enhances the adsorption performance of Cr(VI) on TiO2/BC/g‐C3N4, thereby facilitating its photocatalytic reduction. © 2023 Society of Chemical Industry.

Unveiling the charge migration-induced surface reconstruction of Cu2MoS4 catalyst for boosted CO2 reduction into olefiant gas

Understanding the charge dynamic behavior of the catalyst is crucial to unravel the underlying mechanism for photocatalytic CO2 reduction to C2+ products. However, the structure–activity relationships are not intuitive because of the dynamic evolution of electronic and atomic structures for catalysts under the excitation state. Herein, modeling on layered Cu2MoS4 nanosheets, we for the first time observe charge migration-induced evolution of electronic and atomic structure on Cu2MoS4 catalyst during the CO2 reduction process by combining synchronous-illumination X-ray photoelectron spectroscopy (SI-XPS) with X-ray diffraction (SI-XRD). During the dissociation of CO2 molecules as well as the charge migration process under the visible light irradiation condition, the surface S atoms return back to the lattice phase, leading to the valence-state normalization of Cu, Mo and S atoms and the increases of the interlayer lattice spacing. By virtue of the above unique characteristic changes, Cu2MoS4 nanosheets exhibit excellent activity enhancement (8.7 μmol g−1 h−1) for CO2 reduction to C2H4 under the visible light irradiation in comparison with the trace amount of Cu-doped MoS2 and pure MoS2.

Photocatalytic reduction of 4-nitrophenol over eco-friendly NixCuxFe2O4 without an additional reducing agent in water

Organic pollutants such as 4-nitrophenol (4-NP) pose serious environmental extortions due to their chemical stability for which efficient catalytic materials are indispensable in treating them. In this regard, the present work involves the synthesis of two different types of ferrites (NiFe2O4, and CuFe2O4), and a combination of NixCuxFe2O4 with various ratios that systemically work as efficient photocatalysts without any additional reducing agents is reported. The structural, and morphological properties of NiFe2O4, CuFe2O4, and NiCuFe2O4 were characterized by XRD, FT-IR, SEM, and HRTEM techniques. Then, the catalytic role of individual ferrite catalysts was evaluated towards catalytic reduction of 4-NP under visible light. The progress dye reduction was examined via UV–vis spectrophotometry. The effect of various concentrations, and reduction time were investigated. The kinetic rate constants determined for NiFe2O4, CuFe2O4, and NixCuxFe2O4 revealed that Ni and Cu in bimetallic ferrites promoted the reduction reaction under visible light. The results demonstrated that the photo-reduction efficiency of the Ni0.7Cu0.3Fe2O4 catalyst over 4-NP (conc. 10 ppm) to 4-AP was determined as 82 % under 120 miniutes with good recyclability up to six cycles. The mechanism of photocatalytic reduction of ferrites without the use of a reducing agent was studied. Such facile and productive ferrite materials could be employed as efficient photocatalysts for the reduction of toxic organic contaminants in environmental treatment.

Modifying surface frustrated Lewis pairs of BiOBr by La3+ replacing Bi3+ for expediting CO2 photoreduction

Photocatalytic reduction of carbon dioxide has attracted remarkable attention. However, the photocatalytic efficiency is restricted to the poor capacity of adsorption and activation for CO2 molecules on the surface of catalyst. Herein, La isomorphous substituted BiOBr is prepared by a convenient chemical method with La3+ replacing Bi3+. For CO2 photoreduction, the La-substituted BiOBr shows CO yield of 154.4 μmol·g−1·h−1, being 7.1-fold as higher as original BiOBr. Experimental and calculation results manifest that surface frustrated Lewis acid and base sites of La3+-O2− pairs are formed on the surface of BiOBr with adulteration of La and increased oxygen vacancies, which could be conductive to the adsorption and activation for CO2 molecules. This work not only suggests a possible mechanism for photocatalytic reduction of CO2, but also opens up a new opportunity for the preparation of efficient catalysts for CO2 reduction.

In-situ construction of Bi2WO6/BiOCl p-n heterojunction film for photocatalytic CO2 reduction

Heterojunction composite construction has been considered as a viable method to improve photocatalytic performance. In this study, a kind of highly efficient 2D/0D Bi2WO6/BiOCl p-n heterojunction film with boosted photocatalytic CO2 reduction performance was synthesized on Bi plate via in-situ electrochemical ion-exchange hydrothermal method. Furthermore, the XRD, XPS, SEM, TEM and other techniques were carried out to evaluate as-synthesized films. Our findings indicate that Bi2WO6/BiOCl composite film, with close border contact between Bi2WO6 and BiOCl surfaces, should be conducive to achieve excellent separation and migration of photogenerated charge carriers. Finally, the formation mechanism of p-n heterostructure is demonstrated using XPS core-level alignment method. This work should offer new perspectives into the immobilization method of efficient powder catalysts and the photocatalytic CO2 reduction mechanism of p-n heterojunction films.

Promoting Solar‐driven Hydrogen Peroxide Production over Thiazole‐based Conjugated Polymers via Generating and Converting Singlet Oxygen

AbstractSolar‐driven synthesis of hydrogen peroxide (H2O2) from water and air provides a low‐cost and eco‐friendly alternative route to the traditional anthraquinone method. Herein, four thiazole‐based conjugated polymers (Tz‐CPs: TTz, BTz, TBTz and BBTz) are synthesized via aldimine condensation. BBTz exhibits the highest H2O2 production rate of 7274 μmol g−1 h−1 in pure water. Further, the reaction path is analyzed by electron paramagnetic resonance (EPR), in situ diffuse reflectance infrared Fourier transform (DRIFT) and theoretical calculation, highlighting the prominent role of singlet oxygen (1O2). The generation of 1O2 occurs through the oxidation of superoxide radical (⋅O2−) and subsequent conversion into endoperoxides via [4+2] cycloaddition over BBTz, which promotes charge separation and reduces the barrier for H2O2 production. This work provides new insight into the mechanism of photocatalytic O2 reduction and the molecular design of superior single‐polymer photocatalysts.

Promoting Solar-driven Hydrogen Peroxide Production over Thiazole-based Conjugated Polymers via Generating and Converting Singlet Oxygen.

Solar-driven synthesis of hydrogen peroxide (H2O2) from water and air provides a low-cost and eco-friendly alternative route to the traditional anthraquinone method. Herein, four thiazole-based conjugated polymers (Tz-CPs: TTz, BTz, TBTz and BBTz) are synthesized via aldimine condensation. BBTz exhibits the highest H2O2 production rate of 7274 μmol g-1 h-1 in pure water. Further, the reaction path is analyzed by electron paramagnetic resonance (EPR), in-situ diffuse reflectance infrared fourier transform (DRIFT) and theoretical calculation, highlighting the prominent role of singlet oxygen (1O2). The generation of 1O2 occurs through the oxidation of superoxide radical (•O2-) and subsequent conversion into endoperoxides via [4+2] cycloaddition over BBTz, which promotes charge separation and reduces the barrier for H2O2 production. This work provides new insight into the mechanism of photocatalytic O2 reduction and the molecular design of superior single-polymer photocatalysts.

Uracil derivative-assisted universal synthesis of defective 2-dimensional porous flaky carbon nitride for efficient photocatalytic CO2 reduction

In this paper, three novel defective two-dimensional lamellar carbon nitride were successfully synthesized by molecular self-assembly using melamine and cyanuric acid as supramolecular aggregates and introducing three different uracil derivatives (5-formyluracil, 5-acetyluracil, uracil-5-carboxylic acid). In our previous work, we found that the introduction of thymine into supramolecular precursors has good photocatalytic oxidation ability for NO. On this basis, we discovered that by introducing uracil derivatives as ligands for supramolecular aggregates, not only two-dimensional porous sheet nanostructures can be constructed, but also abundant nitrogen and oxygen defects can be introduced, which is supported by various characterizations. These defects can effectively modulate the electronic structure of carbon nitride and thus improve the separation of photogenerated carriers. In addition, the introduction of uracil derivatives affects the energy band structure of the catalyst, and these are important factors affecting the catalytic activity. Compared with bulk carbon nitride, the synthesized materials exhibited significantly enhanced photocatalytic CO2 reduction activity under mild conditions, with CO yields of 10.34, 28.65, 32.28, and 36.48 μmol g−1h−1 for BCN, CNU2.5, CNF2.5, and CNY2.5, respectively. More importantly, with the support of in situ DRIFTS, we proposed the reaction mechanism of photocatalytic reduction of CO.