Graphitic carbon nitride (g-C3N4 ) has attracted significant attention as an interesting, efficient, and durable carbon-based nanomaterial due to its important characteristics in academia and industry. The g-C3N4 plays a noteworthy role as a catalyst in chemical synthesis due to its high activity, selectivity, and productivity. Herein, we have discussed a variety of carbon-heteroatom bond-forming organic transformations, catalysed by numerous graphitic carbon nitride-based sustainable catalysts to produce biologically active scaffolds. The carbon-based heterogeneous (recyclable and reusable) catalysts exhibited greater catalytic efficiency as compared to traditional catalysts for the fabrication of diverse heterocyclic scaffolds. This chapter demonstrated the versatility of carbon nitride in organic synthesis and the vigorous research activities in the field.

The persistent accumulation of plastic waste poses severe environmental challenges due to its nonbiodegradability and long-term ecological impact. Converting plastic waste into functional carbon nanomaterials represents a sustainable route for waste valorization. In this work, a green carbonization strategy is developed to upcycle single-use plastic waste into oxygen-rich carbon quantum dots (Or-CQDs) for solar-driven photoelectrocatalysis. The synthesized Or-CQDs exhibit excellent hydrophilicity, strong photoluminescence, and a remarkably high oxygen content of 36.8 wt%, predominantly composed of surface hydroxyl and carboxyl functionalities. These oxygenated groups synergistically enhance visible-light absorption, facilitate chargecarrier separation, and promote interfacial oxygen adsorption, enabling efficient metal-free photoelectrocatalytic two-electron oxygen reduction (2e- ORR) under ambient and neutral conditions without sacrificial reagents. The Or-CQDs-based photocathode delivers a high hydrogen peroxide concentration of 140 mmol L- 1 with 95.5% Faradaic efficiency and a quantum yield of 20% at 0.2 V versus NHE, outperforming stateof-the-art oxygen-doped carbon catalysts. Combined experimental and theoretical analyses reveal that oxygenenriched active sites stabilize the *OOH intermediate while suppressing O-O bond cleavage, thereby selectively favoring the 2e- ORR pathway. In situ electrochemical Raman and microsecond-resolved transient absorption spectroscopy confirm sustained reactive oxygen intermediate formation. Additionally, the Or-CQDs demonstrate effective photoelectrocatalytic mineralization of organic pollutants, highlighting their dual functionality in green oxidant production and environmental remediation.

The photocatalytic reduction of CO 2 is a crucial area of research aimed at addressing the dual challenges of mitigating rising CO 2 emissions and producing sustainable chemical feedstocks.While multielectron reduction pathways for CO 2 are well explored,the single electron reduction to produce the highly reactive carbon dioxide radical anion(CO 2 ·- ) remains challenging yet promising for green organic transformations.This review contributes to the field by providing a comprehensive analysis of the mechanisms,materials,and reaction pathways involved in CO 2 ·- generation,focusing on the use of visible-lightdriven photocatalytic materials to circumvent the need for high-energy ultraviolet irradiation.Through a systematic examination of CO 2 ·- production,detection methods,and chemical utilization in photocatalytic carboxylation reactions,this review advances understanding of the chemistry of CO 2 ·- and its applications in sustainable chemical synthesis.In addition,it highlights existing key challenges,such as redox potential limitations,and proposes strategies for scaling up photocatalytic systems to enable practical application.By illuminating the pathway to effectively photocatalyze CO 2 ·- generation and its transformative potential in sustainable chemical synthesis,this review equips scientists with critical insights and strategic approaches for overcoming current limitations,driving innovation in photocatalytic materials for solar-to-chemical energy conversion.

An efficient and environmentally sustainable domino protocol has been presented for the synthesis of spirodihydropyridines with privileged heterocyclic substructures involving a three-component reaction of isatins, β-diketones and 1-naphthylamine using ethanol as a solvent and nanostructured Eu-doped ZnO as recyclable and reusable heterogeneous catalyst. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy were used to characterise the nanostructured catalyst. The doping of europium with ZnO NPs increased catalytic efficiency and provided excellent yields of the products. The present synthetic protocol is most likely the first to explain the synthesis of spirodihydropyridines spiroannulated with chromenoquinolines, pyrimidoquinolines, indenoquinolines and acridines. The synthetic protocol is expected to be extended to synthesise a library of the hybrid molecules of pharmaceutical and medicinal interest and drug discovery research incorporating privileged heterocyclic substructure. This protocol has special features such as operation simplicity, high atom economy, shorter reaction time (10–20 min), mild reaction conditions and excellent yield (80–94

The development of environmentally benign and efficient strategies for synthesizing biologically important heterocycles remains a pivotal challenge in contemporary organic chemistry. Among these, benzimidazole derivatives represent a class of vital heterocyclic compounds with diverse and significant pharmacological applications. This underscores the necessity for advancing sustainable and catalytic methodologies to achieve their efficient and selective synthesis. In this regard, a novel water-assisted strategy has been developed for the synthesis of substituted benzimidazole scaffolds through the reaction of 2-haloanilines, sodium azide, and aldehydes under ultrasound irradiation, catalyzed by a CuO-decked reduced graphene oxide (rGO) nanocomposite in aqueous medium. The CuO-rGO nanocomposite was synthesized via a one-pot chemical route and thoroughly characterized using various analytical techniques. Compared to conventional methods, the CuO-rGO nanocomposite exhibited a 20-fold increase in catalytic activity under ultrasound irradiation. The synergistic effect between water, the catalyst's functionalities, and ultrasound irradiation played a pivotal role in the successful synthesis of the desired products. Furthermore, the catalyst could be easily recovered by centrifugation and reused successfully for up to eight cycles without a loss in activity.

Rational design and precise synthesis of biogenic noble-metal-based catalysts possessing distinctive structure and composition play a crucial role in the chemical industry, enabling sustainable construction of an inclusive range of chemical resources. In this study, we have effectively fabricated Pd@A-CQDs through a straightforward one-pot aqueous protocol assisted by visible light employing renewable biomass-derived amine-rich carbon quantum dots (A-CQDs). The remarkable visible light harnessing capability (bandgap, ca. 2.81 eV), high density (35.7 x 10(18) cm(-3)), and long lifetime (25 ps) of photocharge carriers and amine-rich surface in A-CQDs make them ideal candidates as both reducing and stabilizing agents, thereby facilitating the in situ construction of metallic Pd(0) nanoparticles. Comprehensive physicochemical characterizations have provided compelling evidence for the spherical morphology of Pd@A-CQDs core-shell nanostructures, with ultrathin A-CQDs shells of ca. 1.9 nm and an average diameter of 14 +/- 1 nm. The effectiveness of the synthesized Pd@A-CQDs catalysts was assessed in the ligand- and base-free homocoupling reaction of arylboronic acids in water at ambient temperature. The catalytic tests demonstrated the selective production of the homocoupled compound over protodeboronation products with excellent yield and high catalyst recyclability under ambient conditions. The protocol employed exhibited a high TOF (1.05 x 10(-2) mol g(-1) min(-1)) and a low E-factor, with a remarkably low palladium loading. XPS analysis confirmed the retention of the metallic nature of the palladium core within the catalysts during the reaction. The catalytic function of the palladium core in conjunction with the A-CQDs shell, along with the promotional effects provided by water and oxygen for the formation of nucleophilic tetravalent boron, was conclusively recognized by B-11 NMR and O-2-TPD measurements. The obtained experimental results deliver valuable insights into the probable reaction pathway for the homocoupling reaction catalyzed by the Pd@A-CQDs catalysts. Through a comprehensive and sustainable evaluation, the current methodology exhibits superior performance compared to previously documented techniques in relation to estimated circularity and adherence to good manufacturing practices (GMP).

Cooperative CO2 photoreduction with tailored organic synthesis offers a potent avenue for harnessing concurrently generated electrons and holes, facilitating the creation of both solar fuels and specialized chemical compounds. However, controlling the crystallization and morphologies of metal-free molecular nanostructures with exceptional photocatalytic activities toward CO2 reduction remains a significant challenge. These hurdles encompass insufficient CO2 activation potential, sluggish multielectron processes, delayed charge-separation kinetics, inadequate storage of long-lived photoexcitons, unfavorable thermodynamic conditions, and the precise control of product selectivity. Here, melem oligomer 2D nanosheets (MNSs) synthesized through pyrolysis are transformed into 1D nanorods (MNRs) at room temperature with the simultaneous engineering of vacancies and morphology. Transient absorption spectral analysis reveals that vacancies in MNRs trap charges, extending charge carrier lifetimes. Additionally, carbon vacancies enhance CO2 adsorption by increasing amine functional centers. The photocatalytic performance of MNRs for CO2 reduction coupled with benzyl alcohol oxidation is approximately ten times higher (CH3OH and aromatic aldehyde production rate 27 +/- 0.5 and 93 +/- 0.5 mmol g(-1) h(-1), respectively) than for the MNSs (CH3OH and aromatic aldehyde production rate 2.9 +/- 0.5 and 9 +/- 0.5 mmol g(-1) h(-1), respectively). The CO2 reduction pathway involved the carbon-coordinated formyl pathway through the formation of *COOH and *CHO intermediates, as mapped by in situ Fourier-transform infrared spectroscopy. The superior performance of MNRs is attributed to favorable energy-level alignment, enriched amine surfaces, and unique morphology, enhancing solar-to-chemical conversion.

Despite the growing emphasis on eco-friendly nanomaterials as energy harvesters, scientists are actively searching for metal -free photocatalysts to be used in environmental remediation strategies. Developing renewable resource -based carbon quantum dots (CQDs) as the sole photocatalyst to harvest visible light for efficient pollutant degradation is crucial yet challenging, particularly for addressing the escalating issue of water deterioration. Moreover, the photocatalytic decomposition of H2O2 under visible light irradiation remains an arduous task. Based on this, we designed two types of CQDs, C-CQDs (carboxylic -rich) and A-CQDs (amine -rich) with distinct molecular surfaces. Owing to the higher amount of upward band bending induced by amine -rich molecular surface, A-CQDs efficiently harvest the visible light and prevent recombination kinetics resulting in prolonged lifetimes (25 ps), and augmented charge carrier density (35.7 x 1018) of photoexcited charge carriers. A-CQDs enabled rapid visible -light -driven photolysis of H2O2 (k = 0.058 min -1) and produced higher quantity of center dot OH radicals (0.158 mu mol/sec) for the mineralization of petroleum waste, BETX (i.e. Benzene, Ethylbenzene, Toluene and Xylene) (k = 0.017-0.026 min -1) and real textile wastewater (k = 0.026 min -1). To assess comparative toxicities of both remediated and non-remediated real wastewater samples in a time and dose depended manner, Drosophila melanogaster was used as a model organism. The findings unequivocally demonstrate the potential of remediated wastewater for watering urban forestry.

Developing an efficient heterogeneous photocatalyst for environmental remediation and treatment strategies using visible light harvesting processes is promising but challenging. Herein, Cd1-xCuxS materials have been synthesized and characterized by precise analytical tools. Cd1-xCuxS materials exhibited excellent photocatalytic activity for direct Red 23 (DR-23) dye degradation in visible light irradiation. The operational parameters, like dopant concentration, photocatalyst dose, pH, and initial concentration of dye were investigated during the process. The photocatalytic degradation process follows pseudo-first-order kinetics. As compared to other tested materials, 5% Cu doped CdS material revealed superior photocatalytic performance for the degradation of DR-23 (k = 13.96 x 10-3 min-1). Transient absorption spectroscopy, EIS, PL, and transient photocurrent indicated that adding copper to the CdS matrix improved the separation of photo-generated charge carriers by lowering the recombination rate. Spin-trapping experiments recognized the photodegradation primarily based on secondary redox products, i.e., hydroxyl and superoxide radicals. According to by Mott-Schottky curves, photocatalytic mechanism and photo-generated charge carrier density were elucidated regarding dopant-induced valence and conduction bands shifting. Thermodynamic probability of radical formation in line with the altered redox po-tentials by Cu doping has been discussed in the mechanism. The identification of intermediates by mass spec-trometry study also showed a plausible breakdown mechanism for DR-23. Moreover, samples treated with nanophotocatalyst displayed excellent results when tested for water quality metrics such as DO, TDS, BOD, and COD. Developed nanophotocatalyst shows high recyclability with superior heterogeneous nature. 5% Cu-doped CdS also exhibit strong photocatalytic activity for the degradation of colourless pollutant bisphenol A (BPA) under visible light (k = 8.45 x 10-3 min-1). The results of this study offer exciting opportunities to alter semiconductors' electronic band structures for visible-light-induced photocatalytic activity for wastewater treatment.

Background: A strategy employing water as a hydrogen source is promising but challenging. Conversely, urea is the major pollutants causing substantial water pollution. Moreover, direct reduction of carboxylic acids into aldehydes is still a great challenge due to higher propensity of aldehydes being further reduced to alcohols.Methods: We report a visible-light driven one-step protocol to selectively convert aromatic carboxylic acids to aldehydes with water as the sustainable hydrogen source, environmental pollutant urea as a hole scavenger and Eu3+ doped Na2CaP2O7 phosphor as a viable photocatalyst. Significant findings: Apart from the photocatalytic H2 evolution, the procedure is able to reduce a broad range of carboxylic substrates with good functional group tolerance in good to excellent yield. The insertion of Eu3+ into the present host creates several metastable states inside the forbidden region and thereby led to enhancement of photo stimulation process. Moreover, various experiments and analytical analysis reveal that photo-generated active H-species from water are the direct reducing agent, skipping the use of traditional flammable H2. Pre-sent work provides a 'waste-to-value' route for solar energy driven preparation of valuable chemicals by simultaneous photocatalytic treatment of urea-rich waste water.

Despite the modern boost, developing a new photocatalytic system for the reduction of aldehydes is still challenging due to their high negative reduction potential. Herein, we have used a metal-free photoinduced electron-transfer system based on a cheap and readily available organic dye eosin Y (EY), graphene oxide (GO), and ammonium oxalate (AO) for photocatalytic reduction of structurally diverse aldehydes under sustainable conditions. The protocol shows remarkable selectivity for the photocatalytic reduction of aldehydes over ketones. The decisive interaction of GO and AO with the various states of EY (ground, singlet, triplet, and radical anions), which are responsible for the commencement of the reaction, was examined by various theoretical, optical, electrochemical, and photo-electrochemical studies. The synergetic system of GO, EY, and AO is appropriate for enhancing the separation efficiency of visible-light-induced charge carriers. GO nanosheets act as an electron reservoir to accept and transport photogenerated electrons from the photocatalytic system to the reactant. The reduction of the GO during the process ruled out the back transfer of photoexcited charges. Control experiments explained that the reaction involves two stages: electron transfer and protonation. This process eliminates the necessity of precious-metal-based photocatalysts or detrimental sacrificial agents and overcomes the redox potential limitations for the photoreduction of aldehydes.

Although numerous strategically sound homogeneous photocatalytic C-H bond functionalization have been documented. However, it still lacks versatility somewhere down the line owing to its cost, limited reservoir, poisonousness, product contamination, non-recyclable or non-reusable nature, and insufficient visible light harvesting capacity and photostability of the catalyst. In this regard, nanotechnology and material chemistry advancements make it feasible to create unique forms of nano-photocatalysts, whose photocatalytic properties may be tuned and controlled. In this article, an overview of cutting-edge research endeavors in the field is presented, with a main focus on investigating the scientific and technological potentials of heterogeneous nano-photocatalytic materials in C-H bond functionalization compared to their conventional counterparts. We high -light the band gap structure of nanophotocatalysts compared to the widespread conventional photocatalyst for the potential C-H functionalization. Next, we offer a concise summary of key techniques used to engineer the band gap of bare nanophotocatalysts to facilitate them to efficiently utilize visible light the main component of sunlight. This includes identifying optimal locations for the conduction and valence bands, which produce adequate reducing and oxidizing potentials for the targeted reactions, while also diminishing recombination, promoting high catalytic turnover kinetics, and enabling the efficient separation of charges. Finally, we discuss the illustrative examples of nanophotocatalysts enabling the photo-transformation of C-H bonds under moderate environment. Furthermore, a systematic survey of the mechanisms, reactivity, and applications of this approach has been given, presenting researchers with a fresh viewpoint to discover this promising field and uncover formerly unknown potentials and insights. In addition, this review covers the present obstacles and forthcoming possibilities in this domain.

Despite the fact that carbon quantum dots (CQDs) have significant catalytic potential, only emblematic applications that rely on simple acid-base or hydrogen-bonding activation pathways have been reported. In this study, natural amine-targeted CQDs (NAT-CQDs) have been successfully fabricated using a sustainable technique that harnesses a renewable green source. Based on a holistic sustainable assessment, the present approach for the synthesis of NAT-CQDs surpasses previously reported methods in terms of estimated circular and good-manufacturing-practice metrics. A set of spectroscopic and analytical techniques, including FTIR, XPS, conductometric assay, pH titration, 19FNMR, and 13CNMR confirms the presence of the assessable amino-rich groups (0.0083N) at the surface of NAT-CQDs. The occurrence of surface amine groups unlocked the molecular behavior of as-prepared NAT-CQDs and makes them an unprecedented nanoaminocatalytic platform for the synthesis of diverse pharmacophore scaffolds (>40 examples) via a one-pot Knoevenagel/(aza) Michael addition reaction in water at room temperature. The assessable amine group can covalently activate carbonyl groups through nucleophilic iminium activation modes in water and facilitate the ability to build valuable and therapeutic scaffolds on a gram scale. By transferring significant molecular primacy at the frontier of nanoscale materials, NAT-CQDs can thus bridge the gap between the nanoscale and molecular domains. This protocol can also be applied for the preparation of therapeutic anticoagulant drugs, warfarin, and coumachlor. All the reactions exhibited a high atom economy, low E-factor, low process mass intensity (PMI), high reaction mass efficiency (RME), high carbon efficiency (CE), and high catalyst reusability with overall high sustainable values. NAT-CQDs show high recyclability, and the spectral data of reused catalysts indicate that the NAT-CQDs maintained their surface chemistry and electronic properties, suggesting their stability under the tested conditions. This study presents a remarkable instance of NAT-CQDs showcasing covalent catalysis. Expanding on the aforementioned design concept, the utilization of NAT-CQDs' "potential" as distinct colloidal organocatalysts in aqueous environments at the molecular level introduces valuable prospects for aminocatalytic pathways.

Indeed, all the heterocycles comprises of either "C-C, C-N, C-S or C-O" bonds in their skeleton and construction of these bonds has laid the foundation stone of organic chemistry. The present researchers are continually attempting to develop new strategies for synthesizing miscellaneous structurally divergent molecular entities and these bond forming reactions are the fundamental tools. As a consequence, a colossal upheaval is witnessed in development of benign and sustainable synthetic routes for green bond-forming reactions envisaging carbon-carbon/heteroatom. This chapter is aimed towards highlighting the recent developments perceived in "C-C, C-N, C-S or C-O" bondconstruction especially emphasising greener perspectives i.e. carbocatalysis.

Herein, we demonstrate a simple, reproducible, and environment-friendly strategy for the synthesis of carbon quantum dots (CQDs) utilizing the mango (Mangifera indica) kernel as a renewable green carbon source. Various analytical tools characterized the as-prepared CQDs. These fluorescent CQDs showed significant water solubility with a uniform size of about 6 nm. The as-synthesized CQDs show significantly enhanced catalytic activity for the production of α,β-unsaturated compounds from the derivatives of aromatic alkynes and aldehydes under microwave irradiation in aqueous media. A potential mechanistic pathway and role of carboxylic functionalities were also revealed via various control experiments. The protocol shows outstanding selectivity towards the assessment of α,β-unsaturated compounds over other possible products. A comparative evaluation suggested the as-synthesized CQDs show higher catalytic activity under microwave radiation as compared to the conventional ways. These recyclable CQDs represent a sustainable alternative to metals in synthetic organic chemistry. A cleaner reaction profile, low catalyst loading, economic viability and recyclability of the catalyst, atom economy, and comprehensive substrate applicability are additional benefits of the current protocol according to green chemistry.

Fluorescent carbon quantum dots (CQDs), specified by feature sizes of <10 nm, have become a mystic newcomers in the world of nanoscience and attracted much focus of synthetic chemists since the last decade due to their esoteric physico-chemical features. Because of these magical characteristics, carbon dots-based catalytic systems have unlocked the gateway for eco-friendly, benign, and cost-effective next-generation platform for "Nanocatalysis and Photocatalysis" in organic synthesis. The introduction of CQDs in organic synthesis allows the designing new reactions or catalysis in which unique/unprecedented connection/disconnection of chemical bonds has been implemented for the construction of new molecular architectures. This critical review presents a comprehensive study of the catalytic and photocatalytic efficiency of CQDs in organic synthesis which has initiated a more sustainable strategy in to the catalysis field. By systematic summarization and categorization of various organic transformations such as coupling reactions, oxidation reactions, reduction reactions, condensation reactions, ring-opening reactions, epoxidation, C-H activation, etc., a clear picture of all available catalytic and photocatalytic strategies for CQDs are presented and their unique role in various catalytic approaches for specific reactions are discussed in detail. Catalytic aspects of CQDs in heterocyclic synthesis are also been reviewed. Finally, challenges and future aspects associated with the green catalytic efficiency of CQDs in organic synthesis are highlighted. Herein, this review summarizes the current investigations on CQDs for various organic transformations during last 10 years. We experience that the entire potential of CQDs in organic synthesis has yet to be fully explored in organic synthesis. We hope that this review is serving as a humble urge to encourage other organic chemists for further use of CQDs as a sustainable catalyst in organic synthesis.