Photocatalytic reductive dechlorination of 2-chlorodibenzo-p-dioxin by Pd modified g-C3N4 photocatalysts under UV-vis irradiation: Efficacy, kinetics and mechanism

Photochemical-promoted ZVI reduction for highly efficient removal of 4-chlorophenol and Cr(VI): Catalytic activity, performance and electron transfer mechanisms

Zero-valent iron (ZVI) reduction represents a promising methodology for water remediation, but its broad application is limited by two critical challenges (i.e., aggregation and passivation). Here, we report a hybrid strategy of photochemical-promoted ZVI reduction with high efficiency and reduction capacity for removing coexisting refractory pollutants in water. A composite material with Pd/Fe bimetallic nanoparticles supported onto semiconducting metal oxide (Pd/Fe@WO3-GO) was prepared and subsequently used as the model catalyst. By using the developed strategy with visible light as light source, this catalyst showed a remarkable catalytic performance for simultaneously eliminating 4-chlorophenol (4-CP) and Cr(VI), with dehalogenation rate as high as 0.43 min-1, outperforming the reported ZVI-based catalysts. A synergistic interaction of photocatalysis and ZVI reduction occurred in this strategy, where the interfacial electron transfer on particles surface were greatly strengthened with light irradiation. The activation was attributed to the dual functions of semiconducting material as support to disperse Pd/Fe nanoparticles and as (photoexcited) electron donor to directly trigger reduction reactions and/or indirectly inhibit the formation of oxides passivation layer. Both direct electron transfer and H*-mediated indirect electron transfer mechanisms were confirmed to participate in the reduction of pollutants, while the later was quantitatively demonstrated as the predominant reaction route. Importantly, this strategy showed a wide pH applicability, long-term durability and excellent catalytic performance in different real-water systems. This work provides new insights into ZVI reduction and advances its applications for the removal of combined organic and inorganic pollutants. The developed photochemical-promoted ZVI reduction strategy holds a great potential for practical applications.

Preparation of g-C3N4/TCNQ Composite and Photocatalytic Degradation of Pefloxacin

g-C₃N₄ and g-C₃N₄/TCNQ composites with different doping levels were prepared using the copolymerization thermal method with melamine as a precursor. XRD, FT-IR, SEM, TEM, DRS, PL, and I-T characterized them. The composites were successfully prepared in this study. The photocatalytic degradation of pefloxacin (PEF), enrofloxacin (ciprofloxacin), and ciprofloxacin (ciprofloxacin) under visible light (λ > 550 nm) showed that the composite material had the best degradation effect on PEF. When TCNQ doping is 20 mg and catalyst dosage is 50 mg, the catalytic effect is the best, and the degradation rate reaches 91.6%, k = 0.0111 min^-1, which is four times that of g-C₃N₄. Repeated experiments found that the cyclic stability of the g-C₃N₄/TCNQ composite was good. The XRD images were almost unchanged after five reactions. The radical capture experiments revealed that ·O^2- was the main active species in the g-C₃N₄/TCNQ catalytic system, and h⁺ also played a role in PEF degradation. And the possible mechanism for PEF degradation was speculated.

Graphitic carbon nitride-based photocatalysts in the applications of environmental catalysis

Semiconductor photocatalytic technology has shown great prospects in converting solar energy into chemical energy to mitigate energy crisis and solve environmental pollution problems. The key issue is the development of high-efficiency photocatalysts. Various strategies in the state-of-the-art advancements, such as heterostructure construction, heteroatom doping, metal/single atom loading, and defect engineering, have been presented for the graphitic carbon nitride (g-C₃N₄)-based nanocomposite catalysts to design their surface chemical environments and internal electronic structures to make them more suitable for different photocatalytic applications. In this review, nanoarchitecture design, synthesis methods, photochemical properties, potential photocatalytic applications, and related reaction mechanisms of the modified high-efficiency carbon nitride-based photocatalysts were briefly summarized. The superior photocatalytic performance was identified to be associated with the enhanced visible-light response, fast photoinduced electron-hole separation, efficient charge migration, and increased unsaturated active sites. Moreover, the further advance of the visible-light harvesting and solar-to-energy conversions are proposed.

Selected dechlorination of triclosan by high-performance g-C3N4/Bi2MoO6 composites: Mechanisms and pathways

Environmental-friendly and efficient strategies for triclosan (TCS) removal have received more attention. Influenced by COVID-19, a large amount of TCS contaminants were accumulated in medical and domestic wastewater discharges. In this study, a unique g-C₃N₄/Bi₂MoO₆ heterostructure was fabricated and optimized by a novel and simple method for superb photocatalytic dechlorination of TCS into 2-phenoxyphenol (2-PP) under visible light irradiation. The as-prepared samples were characterized and analyzed by XRD, BET, SEM, XPS, etc. The rationally designed g-C₃N₄/Bi₂MoO₆ (4:6) catalyst exhibited notably photocatalytic activity in that more than 95.5% of TCS was transformed at 180 min, which was 3.6 times higher than that of pure g-C₃N₄ powder. This catalyst promotes efficient photocatalytic electron-hole separation for efficient dechlorination by photocatalytic reduction. The samples exhibited high recyclable ability and the dechlorination pathway was clear. The results of Density Functional Theory calculations displayed the TCS dechlorination selectivity has different mechanisms and hydrogen substitution may be more favorable than hydrogen abstraction in the TCS dechlorination hydrogen transfer process. This work will provide an experimental and theoretical basis for designing high-performance photocatalysts to construct the systems of efficient and safe visible photocatalytic reduction of aromatic chlorinated pollutants, such as TCS in dechlorinated waters.

Efficient Microcystis aeruginosa coagulation and removal by palladium clusters doped g-C3N4 with no light irradiation

Efficient treatment of cyanobacterial blooms in eutrophication waters by safe and reliable nanomaterials is a big challenge for reducing environmental health risks. Herein, a novel strategy combining palladium clusters (Pd_n) with g-C₃N₄ nanocomposite was presented to achieve high-efficient removal of Microcystis aeruginosa cells through coagulation and breakage. Interestingly, 95.17% of algal cells (initial concentration of 5.6 × 10⁶ cells mL^-1) were promptly removed in the Pd/g-C₃N₄ (5%) system within only 10 min and without visible light irradiation and persulfate activation. Both the release of potassium ion and microcystin during the removal process and the transmission electron microscope observations of Microcystis aeruginosa cells proved that the integrity of the algal cell membrane was destroyed. The removal of Microcystin-LR (MC-LR) were further confirmed in the next process. Pd metal interaction and breakage against algal cells may cause disruption of algal cells. This study describes a novel technology for the superfast removal of harmful algae and may provide a new insight into the control of cyanobacterial blooms in practical applications.

Facile Synthesis of ZnO-CeO2 Heterojunction by Mixture Design and Its Application in Triclosan Degradation: Effect of Urea

In this study, simplex centroid mixture design was employed to determine the effect of urea on ZnO-CeO. The heterojunction materials were synthesized using a solid-state combustion method, and the physicochemical properties were evaluated using X-ray diffraction, nitrogen adsorption/desorption, and UV–Vis spectroscopy. Photocatalytic activity was determined by a triclosan degradation reaction under UV irradiation. According to the results, the crystal size of zinc oxide decreases in the presence of urea, whereas a reverse effect was observed for cerium oxide. A similar trend was observed for ternary samples, i.e., the higher the proportion of urea, the larger the crystallite cerium size. In brief, urea facilitated the co-existence of crystallites of CeO and ZnO. On the other hand, UV spectra indicate that urea shifts the absorption edge to a longer wavelength. Studies of the photocatalytic activity of TCS degradation show that the increase in the proportion of urea favorably influenced the percentage of mineralization.

Novel strategies for 2,8-dichlorodibenzo-p-dioxin degradation using ternary Au-modified iron doped TiO2 catalysts under UV-vis light illumination

Polychlorinated dibenzo-p-dioxins (PCDDs), characterized by their extreme toxicity, high persistency and bioaccumulation, regard as one of the most concerned environmental pollutants on the priority list. In this study, microwave-hydrothermal and photoreduction methods were adopted for fabrication of ternary Au@Fe/TiO₂ composites for removal of 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) under UV-Vis light irradiation. The acquired materials were characterized and analyzed by XRD, TEM, XPS, UV-Vis DRS, PL, etc. As a result, the 1%Au@1%Fe/TiO₂ exhibited much higher photocatalytic activity that 96.3% of 2,8-DCDD was removed within 160 min with respect to that of Fe/TiO₂ (3.0 times) and TiO₂ (5.5 times). It revealed the active substances might be produced, which were verified by ESR analysis. In a comparison, the 1%Au@1%Fe/TiO₂ also exhibited high activity in that 97.2% of 2,8-DCDD was removed within 240 min under an anoxic atmosphere. The 1%Au@1%Fe/TiO₂ systems were all pH-dependent that 2,8-DCDD could be fully degraded in neutral conditions. The results of repeatability on 1%Au@1%Fe/TiO₂ showed that the sample was high stability. Fe doping improved the charge separation of TiO₂ and Au modification improved the activity via SPR effect and Mott-Schottky barrier. The degradation mechanisms and pathways were proposed and discussed in detail. The current work develops a new approach on photocatalytic oxidation and reductive dechlorination of dioxins and may open a new opportunity to extend the application range of TiO₂ catalysts.

Optimizing the metal-support interactions at the Pd-polymer carbon nitride Mott-Schottky heterojunction interface for an enhanced electrocatalytic hydrodechlorination reaction

We reported one novel strategy via band engineering of the semiconductor support to optimize the metal-support interactions at a Mott-Schottky heterojunction interface and enhance the metal's electrocatalytic hydrodechlorination (EHDC) performance. Taking palladium-polymer carbon nitride (Pd/PCN) as a model, the band tuning of PCN by heteroatomic phosphorus (P) doping substantially boosted the EHDC of 2,4-dichlorophenol (2,4-DCP, one typical chlorinated organic pollutants (COPs)) on Pd, and a peak specific activity of 0.172 min^-1 cm_Pd^-2 was achieved by Pd/P-PCN-0.25 (0.25 reflected the P content, and denoted the mass ratio of the P source to PCN precursor used in P-PCN synthesis), quadrupling 0.041 min^-1 cm_Pd^-2 of Pd/C and outperforming most of the reported catalysts. The mechanism study revealed the P doping in PCN enabled the positive shift of its Fermi level, which weakened the Pd-PCN interactions and alleviated the electron excess of Pd in Pd/PCN. The P-PCN in Pd/P-PCN-0.25 with the ideal band structure evoked a Pd electronic state that maximized EHDC efficiency. Further investigation into the intermediate products of EHDC on Pd/P-PCN and the biological safety of the 2,4-DCP-contaminated water after EHDC treatment demonstrated the EHDC over our catalyst was environmental-benignity for COPs abatement.

An in situ TEM nanoindentation-induced new nanostructure in cadmium zinc telluride

Phase transformations occurring in a solid govern the structural and physical properties significantly. Nevertheless, deformation-induced phase transition in a soft-brittle solid has not been demonstrated yet. Soft-brittle cadmium zinc telluride (CZT) based instruments have produced technological breakthroughs in the semiconductor industry, and therefore their phase transformations have been widely investigated during the past 60 years. In this study, in situ transmission electron microscopy (TEM) nanoindentation was performed on CZT, and it was found that no brittle fracture occurred at a peak load of 41.9 μN, corresponding to a stress of 1.75 GPa. A new nanostructure induced by in situ TEM nanoindentation was observed, consisting of a single crystal, slip bands, stacking faults, a superlattice, a new tetragonal phase, and Moiré fringes. The new tetragonal phase was formed by partial Cd and Te atoms in the (111[combining macron]) plane slipping along the [1[combining macron]21[combining macron]] orientation, which was elucidated by ab initio simulations. It belongs to a tetragonal crystal system, and the lattice distances along the X and Y axes were 0.382 and 0.376 nm, respectively. Our findings provide new insights into the deformation-induced phase transformation for a soft-brittle solid, and have application potential in solar cells, radiation detectors, and medical imaging, quantum, flexible electronic and optoelectronic devices.

White rot fungus Pleurotus pulmonarius enhanced bioremediation of highly PCDD/F-contaminated field soil via solid state fermentation

This study was performed to evaluate the use of white rot fungus, Pleurotus pulmonarius, to treat polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) in contaminated soil using solid state fermentation (SSF). The soil was collected from a long-closed pentachlorophenol plant in southern Taiwan. The non-sterilized soil with a total PCDD/F concentration of 14,000 ± 2400 ng I-TEQ kg^-1 was mixed directly with the solid fungal inocula at dry w/w ratio of 1:1.4 (ratio-adjusted test) and incubated at 26 ± 2 °C in a controlled environment. The highest PCDD/F decomposition was observed during the mycelium colonization. Pearson correlation coefficient (r) studied during this period (35 days) indicated that laccase had no significant correlation (r = -0.53), while manganese peroxidase had a strong positive correlation (r = 0.88) with PCDD/F decomposition efficiency. After 72 days, the more toxic congeners, tetra- and penta-CDD/Fs were removed to non-detectable levels. Meanwhile, the removal efficiencies of hexa-, hepta-, and octa-CDD/Fs were >80%, >97%, and >90%, respectively. The simultaneous degradation of low and high chlorinated DD/Fs suggested that overall removal was nonspecific. The overall PCDD/F removal was 96%, and the residual concentration (276 ng I-TEQ kg^-1) was below the regulatory control limit (1000 ng I-TEQ kg^-1). In conclusion, this study shows that P. pulmonarius via SSF can successfully remediate the PCDD/F-contaminated field soil. Furthermore, this SSF technique overcame the well-known intractability of PCDD/F biodegradation in non-sterilized soil, making it promising for actual field application.

Theoretical design and experimental investigation on highly selective Pd particles decorated C3N4 for safe photocatalytic NO purification

Rational design of highly active and selective photocatalyst for NO removal is significant for the commercial application of photocatalytic technology because the secondary byproduct caused by insufficient and non-selective pollutant oxidation process is a major challenge. In this work, Pd nanoparticles decorated C₃N₄ (PdCN) is designed by density functional theory (DFT) at first. The PdCN exhibits superiority to CN in terms of both kinetics and thermodynamics performances, as reflected in the lower activation barrier of rate-determining step and higher selectivity for the final product (nitrate) instead of toxic intermediate (NO₂). The as-designed highly selective and efficient photocatalyst is then fabricated by a facile method with an extremely low content of Pd particles supported on C₃N₄. Compared to bare CN, the synthesized PdCN exhibits highly enhanced purification of NO in air and strong inhibition of toxic NO₂ by-product as supported by in-situ DRIFTS investigation, which is consistent with the theoretical prediction. This work is a typical demonstration of setting up a bridge between theory and experiment to give a promising way to the rational design of advanced photocatalysts and atomic understanding of the reaction mechanism.

Dual plasmons-promoted electron-hole separation for direct Z-scheme Bi3O4Cl/AgCl heterojunction ultrathin nanosheets and enhanced photocatalytic-photothermal performance

The dual plasmons (Bi, Ag)-based direct Z-scheme Bi₃O₄Cl/AgCl heterojunction ultrathin nanosheets are successfully synthesized by hydrothermal combined with solid-state reduction strategy. The plasmons Ag and Bi are formed during solid-state reduction process, which are firmly anchored on surface of Bi₃O₄Cl and AgCl, respectively, and favors the charge transfer obviously. Experiments results confirm the formation of heterojunction ultrathin nanosheets with the main size of 200∼300 nm and the thickness of <10 nm. The obtained dual plasmons-based direct Z-scheme Bi₃O₄Cl/AgCl heterojunction ultrathin nanosheets with the band gap of ∼1.66 eV exhibit excellent photothermal performance. 98.3% of Cr (VI) can be photocatalytic reduced and TOC removal rate of ceftriatone sodium reached 98.9% within 210 min, respectively. Due to the surface plasma resonance, the catalyst temperature increases obviously, indicating the enhanced photothermal performance, which is favorable for promoting the photocatalytic performance. Moreover, the cyclic stability experiment also proves the high stability and has advantages in practical applications. The excellent property can be ascribed to the direct Z-scheme accelerating charge transfer and prolonging the lifetimes, the dual plasmons enhancing photothermal performance and the spatial separation of photogenerated charge carriers.

Enhanced photocatalytic reduction for the dechlorination of 2-chlorodibenzo-p-dioxin by high-performance g-C3N4/NiO heterojunction composites under ultraviolet-visible light illumination

Polychlorinated dibenzo-p-dioxins (PCDDs), characterized by their high persistency and bioaccumulation, are widely detected in the environment. In this study, high-performance g-C₃N₄/NiO heterojunctions were fabricated to degrade 2-chlorodibenzo-p-dioxin (2-CDD) under ultraviolet-visible (UV-vis) light illumination. Experiments revealed that the pure g-C₃N₄ and range of g-C₃N₄/NiO heterojunctions were synthesized by the mixing and heating method, and then were characterized by XRD, TEM, XPS and PL etc. The composites exhibited enhanced dechlorination activities under anoxic conditions. After comparison, the g-C₃N₄/NiO (4:6) showed optimal dechlorination performance such that 70.4% of 2-CDD was removed within 8 h and 52.3% of 2-CDD was transformed to dibenzo-p-dioxin (DD), about fourfold higher than the pristine g-C₃N₄. The transformation of 2-CDD was accompanied by the resale of Cl ion, and the additional oxygen was proven to be able to consume electrons and hydrogen ions, thus greatly inhibiting the degradation of PCDD in systems. The g-C₃N₄/NiO (4:6) can be reused at least seven times, and the mechanism was proposed in detail to promote photoinduced electrohole separation and provide active sites. This study extends the use range of g-C₃N₄/NiO heterojunctions and develops a new technology to degrade PCDDs with striking activity and stability.

Interfaces of graphitic carbon nitride-based composite photocatalysts

This review concentrates on the interface issues of g-C₃N₄-based photocatalysts, including methods for constructing interfaces, techniques for identifying interfaces, and the types and roles of the as-developed interfaces.

A Polypyrrole-Modified Pd-Ag Bimetallic Electrode for the Electrocatalytic Reduction of 4-Chlorophenol

A polypyrrole-modified bimetallic electrode composed of Pd-Ag on a Ti substrate (Pd-Ag/PPY/Ti) was successfully prepared via a chemical deposition method, and was applied to the electrocatalytic hydrodechlorination of 4-chlorophenol (4-CP) in aqueous solution. The electrode was characterized by cyclic voltammetry (CV), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Various influences on the dechlorination efficiency of 4-chlorophenol, including applied current, initial pH value, and temperature, were studied. The dechlorination efficiency of 4-CP reached 94% within 120 min under the optimum conditions, i.e., a dechlorination current of 6 mA, an initial pH of 2.30, and a temperature of 303 K. The apparent activation energy of the dechlorination of 4-CP by the Pd-Ag/PPY/Ti electrode was calculated to be 49.6 kJ/mol. The equivalent conversion rate constant kPd was 0.63 L.gPd−1·min−1, which was higher than the findings presented in comparable literature. Thus, a highly effective bimetallic electrode with promising application prospects and low Pd loading was fabricated.

In silico toxicity evaluation of dioxins using structure-activity relationship (SAR) and two-dimensional quantitative structure-activity relationship (2D-QSAR)

Prediction of pEC₅₀ values of dioxins binding with the aryl hydrocarbon receptor (AhR) is of great significance for exploring how dioxins induce toxicity in human body and evaluating their environmental behaviors and risks. To reveal the factors that influence the toxicity of dioxins, provide more accurate mathematical models for predicting the pEC₅₀ values of dioxins, and supplement the toxicity database of persistent organic pollutants, qualitative structure-activity relationship (SAR) and two-dimensional quantitative structure-activity relationship (2D-QSAR) were used in this study. The research objects in this study were 60 organic compounds with pEC₅₀ values and 162 compounds without pEC₅₀ values, which included polychlorinated dibenzofurans (PCDFs), polychlorinated dibenzo-p-dioxins (PCDDs), and polybrominated dibenzo-p-dioxins (PBDDs). The qualitative structure-activity relationship (SAR) was performed first and concluded that halogen substitutions at any of the 2, 3, 7, and 8 sites increased the pEC₅₀ value of the compound. Moreover, two-dimensional quantitative structure-activity relationship (2D-QSAR) models were established by employing multiple linear regression (MLR) method and artificial neural network (ANN) algorithm to investigate the factors affecting the pEC₅₀ values of dioxins molecules. MLR was used to establish the well-understood linear model and ANN was used to establish a more accurate non-linear model. Both models have good fitting, robustness, and predictive ability. Importantly, the ability of dioxins binding to AhR is mainly determined by molecular descriptors including E1m, SM09_AEA (dm), RDF065u, F05 [Cl-Cl], and Neoplastic-80. In addition, the pEC₅₀ values of the 162 dioxins without toxicity data were predicted by MLR and ANN models, respectively.

Quenching-Induced Structural Distortion of Graphitic Carbon Nitride Nanostructures: Enhanced Photocatalytic Activity and Electrochemical Hydrogen Production

Engineered nanomaterials are emerging in the field of environmental chemistry. This study involves the analysis of the structural, electronic, crystallinity, and morphological changes in graphitic carbon nitride (g-C₃N₄), an engineered nanomaterial, under rapid cooling conditions. X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Brunauer-Emmett-Teller, Fourier transform infrared, Raman, band gap, and Mott-Schottky analyses strongly proved that the liquid N₂-quenched sample of g-C₃N₄ has structural distortion. The photocatalytic efficiency of engineered g-C₃N₄ nanostructures was analyzed through the degradation of reactive red 120 (RR120), methylene blue (MB), rhodamine B, and bromophenol as a representative dye. The photocatalytic dye degradation efficiency was analyzed by UV-vis spectroscopy and total organic carbon (TOC) analysis. The photocatalytic efficiency of g-C₃N₄ under different quenching conditions included quenching at room temperature in ice and liquid N₂. The degradation efficiencies are found to be 4.2, 14.7, and 82.33% for room-temperature, ice, and liquid N₂ conditions, respectively. The pseudo-first-order reaction rate of N₂-quenched g-C₃N₄ is 9 times greater than the ice-quenched g-C₃N₄. Further, the TOC analysis showed that 55% (MB) and 59% (RR120) of photocatalytic mineralization were achieved within a time duration of 120 min by the liquid N₂-quenched g-C₃N₄ nanostructure. In addition, the quenched g-C₃N₄ electrocatalytic behavior was examined via the hydrogen (H₂) evolution reaction in acidic medium. The liquid N₂-quenched g-C₃N₄ catalyst showed a lower overpotential with high H₂ evolution when compared with the other two g-C₃N₄-quenched samples. The results obtained provide an insight and extend the scope for the application of engineered g-C₃N₄ nanostructures in the degradation of organic pollutants as well as for H₂ evolution.

TiC doped palladium/nickel foam cathode for electrocatalytic hydrodechlorination of 2,4-DCBA: Enhanced electrical conductivity and reactive activity

Titanium carbide (TiC) with excellent electrical conductivity, chemical and thermal stabilities has been recognized as one of the most promising electrocatalysts. A novel cathode, titanium carbide doped palladium/nickel foam (TiC-Pd/Ni foam), was synthesized via electroless deposition to improve the performance of Pd/Ni foam in electrocatlytic hydrodechlorination (ECH). TiC can be co-precipitated onto the surface of cathode during galvanic replacement reaction between Pd(II) solution and Ni foam. Both constant potential and constant current tests proved that TiC-Pd/Ni foam cathode performed remarkably higher activity for 2,4-dichlorobenzoic acid (2,4-DCBA) than Pd/Ni foam cathode, owing to the excellent conductivity of TiC and enhanced water dissociation over TiC-Pd/Ni foam cathode. Under the optimized reaction conditions of -0.85 V (vs Ag/AgCl), electrolyte of 10 mM and initial pH of 4, 99.8% of aqueous 2,4-DCBA (0.2 mM) was removed within 90 min. The removal process of the aqueous 2,4-DCBA obeyed first-order decay kinetic model. Over 86.3% of 2,4-DCBA can still be removed by TiC-Pd/Ni foam cathode in the fifth consecutive run within 120 min, which was much higher than that of Pd/Ni foam cathode (37.5%). Consequently, TiC-Pd/Ni foam cathode was a promising design for enhanced ECH activity and reduced operation cost.

Carbon nitrides and metal nanoparticles: from controlled synthesis to design principles for improved photocatalysis

The use of sunlight to drive chemical reactions via photocatalysis is of paramount importance towards a sustainable future. Among several photocatalysts, earth-abundant polymeric carbon nitride (PCN, often wrongly named g-C3N4) has emerged as an attractive candidate due to its ability to absorb light efficiently in the visible and near-infrared ranges, chemical stability, non-toxicity, straightforward synthesis, and versatility as a platform for constructing hybrid materials. Especially, hybrids with metal nanoparticles offer the unique possibility of combining the catalytic, electronic, and optical properties of metal nanoparticles with PCN. Here, we provide a comprehensive overview of PCN materials and their hybrids, emphasizing heterostructures with metal nanoparticles. We focus on recent advances encompassing synthetic strategies, design principles, photocatalytic applications, and charge-transfer mechanisms. We also discuss how the localized surface plasmon resonance (LSPR) effect of some noble metals NPs (e.g. Au, Ag, and Cu), bimetallic compositions, and even non-noble metals NPs (e.g., Bi) synergistically contribute with PCN in light-driven transformations. Finally, we provide a perspective on the field, in which the understanding of the enhancement mechanisms combined with truly controlled synthesis can act as a powerful tool to the establishment of the design principles needed to take the field of photocatalysis with PCN to a new level, where the desired properties and performances can be planned in advance, and the target material synthesized accordingly.