Surface-Specific Modification of Graphitic Carbon Nitride by Plasma for Enhanced Durability and Selectivity of Photocatalytic CO2 Reduction with a Supramolecular Photocatalyst

Review of the Versatility and Application Potentials of g-C3N4-Based S-Scheme Heterojunctions in Photocatalytic Antibiotic Degradation

The S-Scheme heterojunction design offers a promising pathway to enhance the photocatalytic activity of semiconductors for antibiotic degradation in aquatic environments. Graphitic carbon nitride (g-C3N4) stands out due to its robust visible light absorption, exceptional charge separation efficiency, and abundant active sites, rendering it an ideal candidate for sustainable and energy-efficient photocatalysis. This review delves into the potential of g-C3N4-based S-Scheme heterojunctions in antibiotic degradation, with a particular emphasis on the photocatalytic principles, inherent advantages, and application prospects. We discuss various semiconductor materials, including metal oxides, multicomponent metal oxides, magnetic oxides, multicomponent magnetic oxides, metal sulfides, and multicomponent metal sulfides, which can be paired with g-C3N4 to fabricate S-Scheme heterojunctions. Furthermore, we explore common preparation techniques for synthesizing g-C3N4-based S-Scheme heterojunction composites, such as the hydrothermal method, solvothermal method, calcination method, self-assembly method, in situ growth, etc. Additionally, we summarize the applications of these g-C3N4-based S-Scheme heterojunctions in the degradation of antibiotics, focusing specifically on quinolones and tetracyclines. By providing insights into the development of these heterojunctions, we actively contribute to the ongoing exploration of innovative technologies in the field of photocatalytic antibiotic degradation. Our findings underscore the vast potential of g-C3N4-based S-Scheme heterojunctions in addressing the challenge of antibiotic contamination in water sources.

Visible-light-responsive hybrid photocatalysts for quantitative conversion of CO2 to highly concentrated formate solutions

Photocatalysts can use visible light to convert CO2 into useful products. However, to date photocatalysts for CO2 conversion are limited by insufficient long-term stability and low CO2 conversion rates. Here we report hybrid photocatalysts consisting of conjugated polymers and a ruthenium(ii)-ruthenium(ii) supramolecular photocatalyst which overcome these challenges. The use of conjugated polymers allows for easy fine-tuning of structural and optoelectronic properties through the choice of monomers, and after loading with silver nanoparticles and the ruthenium-based binuclear metal complex, the resulting hybrid systems displayed remarkably enhanced activity for visible light-driven CO2 conversion to formate. In particular, the hybrid photocatalyst system based on poly(dibenzo[b,d]thiophene sulfone) drove the very active, durable and selective photocatalytic CO2 conversion to formate under visible light irradiation. The turnover number was found to be very high (TON = 349 000) with a similarly high turnover frequency (TOF) of 6.5 s-1, exceeding the CO2 fixation activity of ribulose-1,5-bisphosphate carboxylase/oxygenase in natural photosynthesis (TOF = 3.3 s-1), and an apparent quantum yield of 11.2% at 440 nm. Remarkably, quantitative conversion of CO2 (737 μmol, 16.5 mL) to formate was achieved using only 8 mg of the hybrid photocatalyst containing 80 nmol of the supramolecular photocatalyst at standard temperature and pressure. The system sustained photocatalytic activity even after further replenishment of CO2, yielding a very high concentration of formate in the reaction solution up to 0.40 M without significant photocatalyst degradation within the timeframe studied. A range of experiments together with density functional theory calculations allowed us to understand the activity in more detail.

The Synthesis, Structural Characterization, and DFT Calculation of a New Binuclear Gd(III) Complex with 4-Aacetylphenoxyacetic Acid and 1,10-Phenanthroline Ligands and Its Roles in Catalytic Activity

A new binuclear Gd(III) complex, [Gd2(L)6(Phen)2]·4H2O, was synthesized via the reaction of gadolinium(III) nitrate hexahydrate, 4-acetylphenoxyacetic acid (HL), NaOH, and 1,10-phenanthroline (Phen) in a solution of water-ethanol (v:v = 1:1). The Gd(III) complex was characterized using IR, UV-vis, TG-DSC, fluorescence, and single-crystal X-ray diffraction analyses. The results showed that the Gd(III) complex crystallizes in the triclinic system, space group P-1, and each Gd(III) ion was coordinated with two nitrogen atoms (N1, N2, or N1a, and N2a) from two Phen ligands and seven oxygen atoms (O1, O2, O7a, O9, O8, O8a, O10a, or O1a, O2a, O7, O8, O8a, O9a, and O10) from six L ligands, respectively, forming a nine-coordinated coordination mode. The Gd(III) complex molecules formed a one-dimensional chained and three-dimensional network structure via benzenering π-π stacking. The Hirschfeld surface analysis and the calculations of the electron density distributions of the frontier molecular orbitals of the Gd(III) complex were performed. The catalytic activities of the photocatalytic CO2 reduction and benzyl alcohol oxidation using the Gd(III) complex as a catalyst were performed. The results of the photocatalytic CO2 reduction showed that the yield and the selectivity of CO reached 41.5 μmol/g and more than 99% after four hours, respectively. The results of the benzyl alcohol oxidation showed that the yield of benzaldehyde was 45.7% at 120 °C with THF as the solvent under 0.5 MPa O2 within 2 h.

Polydopamine Coating of Graphitic Carbon Nitride, g-C3N4, Improves Biomedical Application

Graphitic carbon nitride (g-C3N4) is an intriguing nanomaterial that exhibits photoconductive fluorescence properties under UV-visible light. Dopamine (DA) coating of g-C3N4 prepared from melamine was accomplished via self-polymerization of DA as polydopamine (PDA). The g-C3N4 was coated with PDA 1, 3, and 5 times repeatedly as (PDA@g-C3N4) in tris buffer at pH 8.5. As the number of PDA coatings was increased on g-C3N4, the peak intensity at 1512 cm-1 for N-H bending increased. In addition, the increased weight loss values of PDA@g-C3N4 structures at 600 °C from TGA thermograms confirmed that the coating was accomplished. The band gap of g-C3N4, 2.72 eV, was reduced to 0.87 eV after five coatings with PDA. A pristine g-C3N4 was found to have an isoelectric point (IEP) of 4.0, whereas the isoelectric points of 1PDA@g-C3N4 and 3PDA@g-C3N4 are close to each other at 3.94 and 3.91, respectively. On the other hand, the IEP of 5PDA@g-C3N4 was determined at pH 5.75 assuming complete coating with g-C3N4. The biocompatibility of g-C3N4 and PDA@g-C3N4 against L929 fibroblast cell lines revealed that all PDA@g-C3N4 coatings were found to be biocompatible up to a 1000 mg/mL concentration, establishing that PDA coatings did not adversely affect the biocompatibility of the composite materials. In addition, PDA@g-C3N4 was screened for antioxidant potential via total phenol content (TPC) and total flavonoid content assays and it was found that PDA@g-C3N4 has recognizable TPC values and increased linearly with an increased number of PDA coatings. Furthermore, blood compatibility of pristine g-C3N4 is enhanced considerably upon PDA coating, affirmed by hemolysis and the blood clotting index%. Additionally, α-glucosidase inhibitory properties of PDA@g-C3N4 structures revealed that 67.6 + 9.8% of this enzyme was evenly inhibited by 3PDA@g-C3N4 structure.

Synthesis, Structural Characterization, and Hirschfeld Surface Analysis of a New Cu(II) Complex and Its Role in Photocatalytic CO2 Reduction

A new Cu(II) complex, [CuL1L2(CH3COO)2(H2O)]·H2O, was synthesized by the reaction of Cu(CH3COO)2·H2O, 6-phenylpyridine-2-carboxylic acid (HL1), and 4-[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]pyridine (L2) in ethanol-water (v:v = 1:1) solution. The Cu(II) complex was characterized using elemental analysis, IR, UV-vis, TG-DTA, and single-crystal X-ray analysis. The fluorescence properties of the copper complex were also evaluated. The structural analysis results show that the Cu(II) complex crystallizes in the triclinic system with space group P-1. The Cu(II) ion in the complex is five-coordinated with one O atom (O2) and one N atom (N1) from one 6-phenylpyridine-2-carboxylate ligand (L1), one N atom (N2) from 4-[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]pyridine ligand (L2), one O atom (O4) from acetate, and one O atom (O5) from a coordinated water molecule, and it adopts a distorted trigonal bipyramidal geometry. Cu(II) complex molecules form a two-dimensional layer structure through intramolecular and intermolecular O-H…O hydrogen bonding. The two-dimensional layer structures further form a three-dimensional network structure by π-π stacking interactions of aromatic rings. The analysis of the Hirschfeld surface of the Cu(II) complex shows that the H…H contacts made the most significant contribution (46.6%) to the Hirschfeld surface, followed by O…H/H…O, N…H/H…N and C…H/H…C contacts with contributions of 14.2%, 13.8%, and 10.2%, respectively. In addition, the photocatalytic CO2 reduction using Cu(II) complex as a catalyst is investigated under UV-vis light irradiation. The findings reveal that the main product is CO, with a yield of 10.34 μmol/g and a selectivity of 89.4% after three hours.

Synthesis, Structural Characterization, Hirschfeld Surface Analysis, Density Functional Theory, and Photocatalytic CO2 Reduction Activity of a New Ca(II) Complex with a Bis-Schiff Base Ligand

A new bis-Schiff base (L) Ca(II) complex, CaL, was synthesized by the reaction of calcium perchlorate tetrahydrate, 1,3-diamino-2-hydroxypropane, and 2-formyl phenoxyacetic acid in an ethanol-water (v:v = 2:1) solution and characterized by IR, UV-vis, TG-DTA, and X-ray single crystal diffraction analysis. The structural analysis indicates that the Ca(II) complex crystallizes in the monoclinic system, space group P121/n1, and the Ca(II) ions are six-coordinated with four O atoms (O8, O9, O11, O12, or O1, O2, O4, O6) and two N atoms (N1, N2, or N3, N4) of one bis-Schiff base ligand. The Ca(II) complex forms a tetramer by intermolecular O-H…O hydrogen bonds. The tetramer units further form a three-dimensional network structure by π-π stacking interactions of benzene rings. The Hirschfeld surface of the Ca(II) complex shows that the H…H contacts represent the largest contribution (41.6%) to the Hirschfeld surface, followed by O…H/H…O and C…H/H…C contacts with contributions of 35.1% and 18.1%, respectively. To understand the electronic structure of the Ca(II) complex, the DFT calculations were carried out. The photocatalytic CO2 reduction test of the Ca(II) complex exhibited a yield of 47.9 μmol/g (CO) and a CO selectivity of 99.3% after six hours.

The three kingdoms-Photoinduced electron transfer cascades controlled by electronic couplings

Excited states are the key species in photocatalysis, while the critical parameters that govern their applications are (i) excitation energy, (ii) accessibility, and (iii) lifetime. However, in molecular transition metal-based photosensitizers, there is a design tension between the creation of long-lived excited (triplet), e.g., metal-to-ligand charge transfer (3MLCT) states and the population of such states. Long-lived triplet states have low spin-orbit coupling (SOC) and hence their population is low. Thus, a long-lived triplet state can be populated but inefficiently. If the SOC is increased, the triplet state population efficiency is improved-coming at the cost of decreasing the lifetime. A promising strategy to isolate the triplet excited state away from the metal after intersystem crossing (ISC) involves the combination of transition metal complex and an organic donor/acceptor group. Here, we elucidate the excited state branching processes in a series of Ru(II)-terpyridyl push-pull triads by quantum chemical simulations. Scalar-relativistic time-dependent density theory simulations reveal that efficient ISC takes place along 1/3MLCT gateway states. Subsequently, competitive electron transfer (ET) pathways involving the organic chromophore, i.e., 10-methylphenothiazinyl and the terpyridyl ligands are available. The kinetics of the underlying ET processes were investigated within the semiclassical Marcus picture and along efficient internal reaction coordinates that connect the respective photoredox intermediates. The key parameter that governs the population transfer away from the metal toward the organic chromophore either by means of ligand-to-ligand (3LLCT; weakly coupled) or intra-ligand charge transfer (3ILCT; strongly coupled) states was determined to be the magnitude of the involved electronic coupling.