Transition metals-doped g-C3N4 nanostructures as advanced photocatalysts for energy and environmental applications.

Graphitic carbon nitride (g-C3N4)-based heterostructured photocatalysts have received significant attention for its potential applications in the treatment of wastewater and hydrogen evolution. The utilization of semiconductor materials in heterogeneous photocatalysis has recently received great attention due to their potential and eco-friendly properties. Doping with metal ions plays a crucial role in altering the photochemical characteristics of g-C3N4, effectively enhancing photoabsorption into the visible range and thus improving the photocatalytic performance of doped photocatalysts. As an emerging nanomaterial, nanostructured g-C3N4 represents a visible light-active semiconducting photocatalyst that has attracted significant interest in the photocatalysis field, particularly for its practical water treatment applications. To the best of our knowledge, investigations of functionalized photocatalytic (PC) materials on 3d transition metal-doped g-C3N4 remain unexplored in the existing literature. g-C3N4 based heterohybrid photocatalysts have demonstrated excellent reusability, making them highly promising for wastewater treatment applications. This paper describes the overview of numerous studies conducted on the heterostructured g-C3N4 photocatalysts with various 3d metals. Research studies have revealed that the introduction of element doping with various 3d transition metals (e.g., Ti, Mn, Fe, Co, Ni, Cu, Zn, etc.) into g-C3N4 is an efficient approach to enhance degradation efficacy and boost photocatalytic activity (PCA) of doped g-C3N4 catalysts. Moreover, the significance of g-C3N4 heterostructured nanohybrids is highlighted, particularly in the context of wastewater treatment applications. The study concludes by providing insights into future perspectives in this developing area of research, with a specific focus on the degradation of various organic contaminants.

Crystal structure of ethyl 5-acetyl-2-{[(di-methyl-amino)-methyl-idene]amino}-4-methyl-thio-phene-3-carboxyl-ate.

In the title thio-phene derivative, C13H18N2O3S, the dihedral angles between the thio-phene ring and the [(di-methyl-amino)-methyl-idene]amino side chain (r.m.s. deviation = 0.009 Å) and the -CO2 ester group are 3.01 (16) and 59.9 (3)°, respectively. In the crystal, inversion dimers linked by pairs of C-H⋯O hydrogen bonds generate R 2 (2)(16) loops. The dimers are linked by another weak C-H⋯O inter-action, forming chains along [001]. In addition, weak C-H⋯π inter-actions are observed, which link the chains into (001) layers.

Crystal structure of ethyl 5-[3-(di-methyl-amino)-acrylo-yl]-2-{[(di-methyl-amino)-methyl-idene]-amino}-4-methylthio-phene-3-carb-oxy-late.

In the title compound, C16H23N3O3S, the dihedral angles between the thio-phene ring and the almost planar di-methyl-amino-methyl-ene-amino (r.m.s. deviation = 0.005 Å) and di-methyl-amino-acryloyl (r.m.s. deviation = 0.033 Å) substituents are 6.99 (8) and 6.69 (7)°, respectively. The ester CO2 group subtends a dihedral angle of 44.92 (18)° with the thio-phene ring. An intra-molecular C-H⋯O hydrogen bond generates an S(6) ring. In the crystal, inversion dimers linked by pairs of C-H⋯O hydrogen bonds generate R (2) 2(14) loops. In addition, a weak C-H⋯π inter-action is observed.

Crystal structure of ethyl 5-(3-fluoro-phen-yl)-2-[(4-fluoro-phen-yl)methyl-idene]-7-methyl-3-oxo-2H,3H,5H-[1,3]thia-zolo[3,2-a]pyrimidine-6-carboxyl-ate.

In the title mol-ecule, C23H18F2N2O3S, the pyrimidine ring is in a half-chair conformation and the 3-fluoro-phenyl group is in the axial position. The thia-zole ring (r.m.s. deviation = 0.0252 Å) forms dihedral angles of 84.8 (7) and 9.6 (7)° with the 3-fluoro-substituted and 4-fluoro-substituted benzene rings, respectively. In the crystal, weak C-H⋯F and C-H⋯O hydrogen bonds connect mol-ecules, forming zigzag chains along the b axis. In addition π-π stacking inter-actions with a centroid-centroid distance of 3.7633 (9) Šconnect these chains into ladders via inversion-related 4-fluoro-phenyl groups.

Crystal structure of 2-acetyl-5-(3-methoxyphenyl)-3,7-dimethyl-5H-1,3-thiazolo[3,2-a]pyrimidine-6-carboxylate.

In the title mol-ecule, C20H22N2O4S, the pyrimidine ring is in a flattened half-chair conformation and the 3-meth-oxyphenyl substituent is in an axial arrangement. The thia-zole ring forms a dihedral angle of 81.3 (1)° with the benzene ring. In the crystal, weak C-H⋯S inter-actions link mol-ecules into chains along [001]. In addition, there are π-π inter-actions between inversion-related thia-zole rings with a centroid-centroid distance of 3.529 (2) Å. The ethyl group was refined as disordered over two sets of sites with an occupancy ratio of 0.52 (3):0.48 (2).

Methyl 4-(4-hy-droxy-phen-yl)-6-methyl-2-sulfanyl-idene-1,2,3,4-tetra-hydro-pyrimidine-5-carboxyl-ate.

In the title mol-ecule, C13H14N2O3S, the di-hydro-pyrimidine ring is in a flattened sofa conformation, with the methine C atom forming the flap. The dihedral angle between the mean plane of the five essentially planar atoms of the di-hydro-pyrimidine ring [maximum deviation = 0.056 (4) Å] and the benzene ring is 89.4 (2)°. The O atom of the carbonyl group is in a trans conformation with respect to the C=C bond of the di-hydro-pyrimidine ring. In the crystal, N-H⋯O and O-H⋯S hydrogen bonds connect mol-ecules, forming a two-dimensional network parallel to (001).

Crystal structure of 1-(2,4-di-methyl-phen-yl)-2-(4-tri-methyl-silyl-1H-1,2,3-triazol-1-yl)ethanone.

The asymmetric unit of the title compound, C15H21N3OSi, contains two mol-ecules with similar conformations (r.m.s. overlay fit for the 20 non-H atoms = 0.163 Å). The dihedral angles between the planes of the 1,2,3-triazole and 2,4-di-methyl-benzene rings are 27.0 (3) and 19.5 (3)°. In the crystal, mol-ecules are linked by very weak C-H⋯O and C-H⋯N hydrogen bonds to generate [100] chains. The chains are cross-linked by C-H⋯π inter-actions.

Methyl 5-(4-acet-oxy-phen-yl)-2-(2-bromo-benzyl-idine)-7-methyl-3-oxo-2,3-di-hydro-5H-1,3-thia-zolo[3,2-a]pyrimidine-6-carboxyl-ate.

In the title mol-ecule, C24H19BrN2O5S, the pyrimidine ring is in a flattened half-chair conformation and the 4-acet-oxy-phenyl group is substituted axially to this ring. The thia-zole ring is essentially planar [with a maximum deviation of 0.012 (2) Šfor the N atom] and forms dihedral angles of 17.65 (13) and 88.95 (11)° with the bromo- and acet-oxy-substituted benzene rings, respectively. The dihedral angle between the benzene rings is 81.84 (13) Å. In the crystal, pairs of weak C-H⋯O hydrogen bonds lead to the formation of inversion dimers. A weak C-H⋯π inter-action and π-π stacking inter-actions with centroid-centroid distances of 3.5903 (14) Šare observed.

4-Bromo-methyl-6-tert-butyl-2H-chromen-2-one.

In the crystal structure of the title compound, C14H15BrO2, weak C-H⋯O inter-actions link the mol-ecules into zigzag chains extending along the c-axis direction. These chains are further assembled into (100) layers via π-π stacking inter-actions between inversion-related chromenone fragments [inter-planar distance = 3.376 (2) Å].

2-(3,4-Di-fluoro-phen-yl)-1H-benzimidazole.

In the title mol-ecule, C13H8F2N2, the dihedral angle between the benzimidazole ring system and the di-fluoro-substituted benzene ring is 30.0 (1)°. In the crystal, mol-ecules are linked by N-H⋯N hydrogen bonds, forming chains along [010]. In addition, weak C-H⋯F hydrogen bonds connect chains into a two-dimensional network parallel to (001). A weak C-H⋯π inter-action is observed between an H atom of the benzimidazole ring sytem and the π system of the di-fluoro-substituted benzene ring.

Ethyl 3-eth-oxy-carbonyl-methyl-7-methyl-5-phenyl-5H-thia-zolo[3,2-a]pyrimidine-6-carboxyl-ate.

In the title compound, C(20)H(22)N(2)O(4)S, the central pyrimidine ring incorporating a chiral C atom is significantly puckered and adopts a slight boat conformation with C atom bearing the phenyl ring and the N atom opposite displaced by 0.367 (2) and 0.107 (2) Å, respectively, from the plane formed by the remaining ring atoms. The benzene ring is positioned axially to the pyrimidine ring, making a dihedral angle of 88.99 (5)°. The thia-zole ring is essentially planar (r.m.s. deviation = 0.0033 Å). In the crystal, pairs of C-H⋯O inter-actions result in centrosymmetric dimers with graph-set motifs R(1) (2)(7) and R(2) (2)(8). A weak C-H⋯π contact is also observed.

Ethyl 3-acetyl-4-(3-meth-oxy-phen-yl)-6-methyl-2-sulfanyl-idene-1,2,3,4-tetra-hydro-pyrimidine-5-carboxyl-ate.

In the title compound, C(17)H(20)N(2)O(4)S, the aryl ring is positioned perpendicular to the dihydro-pyrimidine ring, the dihedral angle between the ring planes being 77.48 (9)°. The carboxyl-ate and methyl groups are in a cis conformation with respect to the C=C bond. The dihydro-pyrimidine ring adopts a twist-boat conformation. The crystal structure is stabilized by N-H⋯O and C-H⋯O inter-actions, the former resulting in mol-ecular chains along the b axis and the latter forming inversion dimers.

Methyl 2-(2-bromo-benzyl-idene)-5-(4-hy-droxy-phen-yl)-7-methyl-3-oxo-2,3-dihydro-5H-1,3-thia-zolo[3,2-a]pyrimidine-6-carboxyl-ate.

In the title compound, C(22)H(17)BrN(2)O(4)S, the central dihydropyrimidine ring, with a chiral C atom, is significantly puckered and adopts a half-chair conformation with the chiral C atom displaced from the mean plane of the remaining ring atoms by 0.305 (6) Å. The hydroxy-phenyl ring is positioned axially to the pyrimidine ring and almost bisects it, the dihedral angle between the mean-planes of the two rings being 89.78 (12)°. The meth-oxy-carbonyl group is disordered over two sites with an occupancy ratio of 0.568 (5):0.432 (5), resulting in a major and a minor conformer. In the crystal, O-H⋯N and C-H⋯S inter-actions result in sheets along the c axis. The supra-molecular assembly is stabilized by π-π stacking inter-actions between the 2-bromo-benzyl-idene and thia-zolopyrimidine rings [centroid-centroid distance = 3.632 (1) Å]. In addition, C-H⋯π inter-actions are also observed in the crystal structure.

Methyl 5-(4-hy-droxy-3-meth-oxy-phen-yl)-2-(4-meth-oxy-benzyl-idene)-7-methyl-3-oxo-2,3-dihydro-5H-thia-zolo[3,2-a]pyrimidine-6-carboxyl-ate.

In the title compound, C(24)H(22)N(2)O(6)S, a pyrimidine ring substituted with 4-hy-droxy-3-meth-oxy-phenyl is fused with a thia-zole ring. The 4-hy-droxy-3-meth-oxy-phenyl group is positioned axially to the pyrimidine ring, making a dihedral angle 85.36 (7)°. The pyrimidine ring adopts a twist boat conformation. In the crystal, O-H⋯N inter-actions result in a chain running along the b axis. The carbonyl O atom bonded to the thia-zole ring is involved in two C-H⋯O hydrogen-bond inter-actions forming centrosymmetric dimers; the ten- and six-membered rings resulting from these inter-actions have R(2) (2)(10) and R(1) (2)(6) motifs, respectively.