Nitrogen-Doped Graphene Aerogel toward Efficient Solar Steam Generation: Synergistic Effects of Thermal Conductivity and Wettability

Solar-driven interfacial evaporation technology is regarded as a promising strategy for global freshwater shortage owing to its green and sustainable desalination process. Graphene aerogel (GA) is widely utilized in the design of solar-driven steam generation systems due to its excellent photothermal conversion efficiency and broad spectral absorption. Given the significant impact of hydrophilicity and thermal insulation on the performance of evaporators, nitrogen doping in the graphene structure not only effectively enhances its wettability but also allows for moderate tuning of its thermal conductivity, thereby optimizing the overall performance of the evaporator. Therefore, graphene oxide (GO) and ethylenediamine were used to prepare nitrogen-doped graphene aerogel (NGA) via a one-step hydrothermal method. Experimental investigations and molecular dynamics (MD) simulations were employed to explore the effects of varying nitrogen-doping concentrations on the thermal conductivity and wettability of NGA. The results revealed that as the nitrogen-doping concentration increased, the aerogel exhibited enhanced wettability, while the thermal conductivity initially decreased and then increased. This phenomenon is attributed to the fact that improved wettability can hinder heat convection, resulting in reduced heat transfer efficiency. However, further enhancement in wettability reduces the solid-liquid interfacial thermal resistance, thereby boosting heat transfer performance. Consequently, NGA-2, with an optimal nitrogen-doping concentration, demonstrated superior evaporation performance, achieving a high evaporation rate of 1.64 kg m-2 h-1 and an outstanding evaporation efficiency of 92.2% under one-sun irradiation. This study highlights the improved performance of solar evaporators through the synergistic effects of heat and mass transfer, underscoring their significant potential in seawater desalination applications.

Harnessing Hole Sites in 2D Monolayer C60 for Metal Cluster Anchoring

Synthesis of 2D quasi-hexagonal phase C60 (qHP C60) has opened avenues for its application as a novel catalytic support. This study investigates the structure, stability, and anisotropic properties of Cu4 clusters anchored on the qHP C60 surface through density functional theory calculations. Our findings reveal that the Cu4 cluster preferentially occupies the intrinsic holes of the qHP C60 via one of its tetrahedral faces, resulting in enhanced stability and conductivity, with a significantly reduced band gap of 0.11 eV, compared to the semiconductor behavior of pristine qHP C60. The anisotropic mechanical properties are retained, affirming the robustness of the material under stress. Importantly, the interaction between qHP C60 and Cu4 not only modifies intramolecular bonding but also introduces additional active sites, thereby having a promising enhanced catalytic performance. This work underscores the potential of qHP C60 as an innovative support in catalysis, paving the way for further exploration of its capabilities in industrial applications.

Launching Graphene into 3D Space: Symmetry, Topology, and Strategies for Bottom-Up Synthesis of Schwarzites

Schwarzites are hypothetical carbon allotropes in the form of a continuous negatively curved surface with three-dimensional periodicity. These materials of the future attract interest because of their anticipated large surface area per volume, high porosity, tunable electric conductivity, and excellent mechanical strength combined with light weight. A three-decade-long history attempting schwarzite synthesis from gas-phase carbon atoms went without success. Design of schwarzites is both a digital art and the science of placing tiles of sp2-carbon polygons on mathematically defined triply periodic minimal surfaces. The knowledge of how to connect polygons in sequence using the rules of symmetry unlocks paths for the bottom-up synthesis of schwarzites by organic chemistry methods. Schwarzite tiling by heptagons is systematically analyzed and classified by symmetry and topology. For the first time, complete plans for the bottom-up synthesis of many schwarzites are demonstrated. A trimer of heptagons is suggested as the key building block for most synthetic schemes.

Building hydrophobic substrate pocket to boost activity of laccase-like nanozyme through acetonitrile-mediated strategy

Nanozymes, as promising alternatives to natural enzymes, offer several advantages with biocatalytic functions but remain inferior in catalytic activity. It is crucial to focus on factors that affect the enzymatic activity of nanozymes and develop strategies to make them more competitive with natural enzymes. Herein, CuV2O5 nanorods are confirmed to own the intrinsic laccase-like activity, and an acetonitrile (MeCN)-mediated strategy is proposed for reaction acceleration by mimicking the enzymatic substrate pocket. In the presence of MeCN, the interaction between substrates and nanozymes gets efficiently promoted by the bridging function of cyano-group, where the utilization of Cu active sites is greatly improved due to the condensed hydrophobic substrate layers formed in the vicinity of CuV2O5 nanorods by the solvent effect of MeCN. Theoretical calculations also disclose that the addition of MeCN endows 2,4-dichlorophenol (2,4-DP) with a lower free-energy barrier in adsorption and activation on the surface of CuV2O5 nanozyme. Benefiting from the improved activity, a sensitive colorimetric sensing platform for 2,4-DP is constructed with the limit of detection as low as 0.48 μM. Our finding lays a theoretical foundation for achieving high-performance catalytical activity of the nanozymes based on the modulation of the reaction microenvironment, effectively alleviating the complex engineering process of nanozymes.

Graphene-Based Catalysts: Emerging Applications and Potential Impact

Carbon nanofillers in general and graphene in particular are considered as promising potential candidates in catalysis due to their two-dimensional (2D) nature, zero bandwidth, single atom thickness with a promising high surface area: volume ratio. Additionally, graphene oxide via result of tunable electrical properties has also been developed as a catalytic support for metal and metal oxide nanofillers. Moreover, the possession of higher chemical stability followed by ultrahigh thermal conductivity plays a prominent role in promoting higher reinforcement of catalytically active sites. In this review we have started with an overview of carbon nanofillers as catalyst support, their main characteristics and applications for their use in heterogeneous catalysis. The review article also critically focusses on the catalytic properties originating from both functional groups as well as doping. An in-depth literature on the various reaction catalysed by metal oxide based nanoparticles supported on GO/rGO has also been incorporated with a special focus on the overall catalytic efficiency with respect to graphene contribution. The future research prospective in the aforementioned field has also been discussed.

A First Principles Study of Lithium Adsorption in Nanoporous Graphene

Recently, nanoporous graphene has attracted great interest in the scientific community. It possesses nano-sized holes; thus, it has a highly accessible surface area for lithium adsorption for energy storage applications. Defective graphene has been extensively studied. However, the lithium adsorption mechanism of nanoporous graphene is not clearly understood yet. Here, we present theoretical investigations on the lithium-ion adsorption mechanism in nanoporous graphene. We perform ab initio electronic structure calculations based on density functional theory. Lithium adsorption in a graphene nanopore is studied and adsorption sites are determined. We also study different lithium-ion distributions in graphene nanopores to determine the best lithium-nanoporous graphene structures for lithium-ion batteries. We show that lithium ions can be adsorbed in a graphene nanopore, even in a single layer of graphene. It is also shown that adding more nanopores to multilayer nanoporous graphene can result in higher Li storage capacity for new-generation lithium-ion batteries.

Core-Shell Semiconductor-Graphene Nanoarchitectures for Efficient Photocatalysis: State of the Art and Perspectives

Semiconductor photocatalysis holds great promise for renewable energy generation and environment remediation, but generally suffers from the serious drawbacks on light absorption, charge generation and transport, and structural stability that limit the performance. The core-shell semiconductor-graphene (CSSG) nanoarchitectures may address these issues due to their unique structures with exceptional physical and chemical properties. This review explores recent advances of the CSSG nanoarchitectures in the photocatalytic performance. It starts with the classification of the CSSG nanoarchitectures by the dimensionality. Then, the construction methods under internal and external driving forces were introduced and compared with each other. Afterward, the physicochemical properties and photocatalytic applications of these nanoarchitectures were discussed, with a focus on their role in photocatalysis. It ends with a summary and some perspectives on future development of the CSSG nanoarchitectures toward highly efficient photocatalysts with extensive application. By harnessing the synergistic capabilities of the CSSG architectures, we aim to address pressing environmental and energy challenges and drive scientific progress in these fields.

Chemical Intercalation of Layered Materials: From Structure Tailoring to Applications

The intercalation of layered materials offers a flexible approach for tailoring their structures and generating unexpected properties. This review provides perspectives on the chemical intercalation of layered materials, including graphite/graphene, transition metal dichalcogenides, MXenes, and some particular materials. The characteristics of the different intercalation methods and their chemical mechanisms are discussed. The influence of intercalation on the structural changes of the host materials and the structural change how to affect the intrinsic properties of the intercalation compounds are discussed. Furthermore, a perspective on the applications of intercalation compounds in fields such as energy conversion and storage, catalysis, smart devices, biomedical applications, and environmental remediation is provided. Finally, brief insights into the challenges and future opportunities for the chemical intercalation of layered materials are provided.

Catalytic system having an organotellurium ligand on graphene oxide: immobilization of Pd(0) nanoparticles and application in heterogeneous catalysis of cross-coupling reactions

First heterogeneous catalytic system, having a covalently linked hybrid bidentate organotellurium ligand [i.e., PhTe-CH2-CH2-NH2] on the surface of graphene oxide, has been synthesized with immobilized and stabilized Pd(0) nanoparticles. To the best of our knowledge, it is the first such catalytic system in which a heterogenized organotellurium ligand has been used. It has been well-characterized using different physicochemical characterization techniques viz. P-XRD, XPS, HR-TEM, EELS, FE-SEM, EDX, TGA, BET surface area analysis, FT-IR spectroscopy, and Raman spectroscopy. The Pd content of the final system has been quantified using ICP-OES. Its applications have been explored in Suzuki-Miyaura C-C cross coupling and C-O cross coupling reactions. Hot filtration experiments corroborate the heterogeneous nature of the catalysis. It is recyclable for up to five reaction cycles in Suzuki-Miyaura and C-O cross coupling with marginal loss in performance. It also catalyzes the reactions of chloroarenes such as chlorobenzene, 4-chloroaniline, 1-chloro-4-nitrobenzene, 4-chloroacetophenone, 4-chlorobenzophenone for Suzuki coupling, and 1-chloro-4-nitrobenzene, 4-chlorobenzonitrile, chlorobenzene, and 4-chlorotoluene for C-O coupling. P-XRD, FE-SEM, and EDX study reveals that the catalytic system retains its structural originality and functionality after recycling.

Synthesis of magnetic Fe3O4/graphene aerogel for the removal of 2,4-dichlorophenoxyacetic acid herbicide from water

Graphene-based aerogels are among the lightest materials in the world and have been extensively studied for environmental remediation. In this work, an Fe3O4/graphene aerogel material was synthesized using the co-precipitation method. The prepared material was characterized using X-ray diffraction (XRD), scanning electron microscopy/X-ray energy dispersive spectroscopy (FESEM/EDX), infrared spectroscopy (FT-IR), and vibration sample magnetization (VSM). The results showed that the Fe3O4 nanoparticles with a particle size of less than 100 nm were well-distributed on the surface of the graphene aerogel. The prepared Fe3O4/graphene aerogel showed effective removal of 2,4-D herbicide from the aqueous solution with a maximal adsorption capacity of approximately 42.918 mg g-1. The adsorption isotherms and kinetics were investigated to study the adsorption behaviour of the resultant material. The saturation magnetism value of the aerogel was determined to be about 20.66 emu g-1, indicating that the adsorbent could be easily collected from the solution using an external magnet. These results implied that the prepared Fe3O4/graphene aerogel could be a promising adsorbent for the removal of 2,4-D herbicide from water.

Electron transfer enhanced catalytic activity of nitrogen doped reduced graphene oxide supported CuCo2O4 towards the fast reduction of 4-nitrophenol in water

There has been a growing interest in the design and development of graphene based composite materials with superior performances for environmental catalytic applications. But in most of the studies the synthesis conditions require elevated temperatures and expensive working setups (high temperature furnaces, autoclaves, inert atmosphere conditions etc.). In this reported work, the nitrogen doped reduced graphene oxide supported CuCo2O4 (NG/CuCo2O4) composites were prepared through a simple one pot synthesis method under mild conditions (∼95 °C and air atmosphere) and successfully employed as catalysts for the reduction of toxic 4-nitrophenol (4NP). The characterization results revealed the successful formation of NG/CuCo2O4 composites with a possible charge transfer interaction between nitrogen doped reduced graphene oxide support of CuCo2O4. The NG/CuCo2O4 hybrids exhibited robust catalytic activity in 4NP reduction with an activity factor of 261.5 min-1 g-1. A 4NP conversion percentage which is as high as 99.5% was achieved within 11 min using the NG/CuCo2O4 catalyst. The detailed kinetic analysis confirmed the Langmuir-Hinshelwood model for the NG/CuCo2O4 catalysed 4NP reduction. The nitrogen doped reduced graphene oxide support modified the electronic levels of CuCo2O4 nanoparticles through electron transfer interactions and enhanced the catalytic activity of CuCo2O4 in NG/CuCo2O4 through improved adsorption of reactant ions and effective generation of active hydrogen species. The good reusability and stability along with profound activity of NG/CuCo2O4 catalyst makes it a promising material for wide scale catalytic applications.

Exploring Enhanced Hydrolytic Dehydrogenation of Ammonia Borane with Porous Graphene-Supported Platinum Catalysts

Graphene is a good support for immobilizing catalysts, due to its large theoretical specific surface area and high electric conductivity. Solid chemical converted graphene, in a form with multiple layers, decreases the practical specific surface area. Building pores in graphene can increase specific surface area and provide anchor sites for catalysts. In this study, we have prepared porous graphene (PG) via the process of equilibrium precipitation followed by carbothermal reduction of ZnO. During the equilibrium precipitation process, hydrolyzed N,N-dimethylformamide sluggishly generates hydroxyl groups which transform Zn2+ into amorphous ZnO nanodots anchored on reduced graphene oxide. After carbothermal reduction of zinc oxide, micropores are formed in PG. When the Zn2+ feeding amount is 0.12 mmol, the average size of the Pt nanoparticles on PG in the catalyst is 7.25 nm. The resulting Pt/PG exhibited the highest turnover frequency of 511.6 min-1 for ammonia borane hydrolysis, which is 2.43 times that for Pt on graphene without the addition of Zn2+. Therefore, PG treated via equilibrium precipitation and subsequent carbothermal reduction can serve as an effective support for the catalytic hydrolysis of ammonia borane.

Catalytic selectivity of nanorippled graphene

Experiments have shown that nanoscale ripples in a graphene membrane exhibit unexpectedly high catalytic activity with respect to hydrogen dissociation. Nonetheless, the catalytic selectivity of nanorippled graphene remains unknown, which is an equally important property for assessing a catalyst's potential and its fit-for-purpose applications. Herein, we examine the catalytic selectivity of nanorippled graphene using a model reaction of molecular hydrogen with another simple but double-bonded molecule, oxygen, and comparing the measurement results with those from splitting of hydrogen molecules. We show that although nanorippled graphene exhibits a high catalytic activity toward hydrogen dissociation, the activity for catalyzing the hydrogen-oxygen reaction is quite low, translating into a strong catalytic selectivity. The latter reaction involves the reduction of oxygen molecules by the dissociated hydrogen adatoms, which requires additional energy cost and practically determines the selectivity. In this sense, the well-established information about reactions in general of atomic hydrogen with many other species in the literature could potentially predict the selectivity of nanorippled graphene as a catalyst. Our work provides implications for the catalytic properties of nanorippled graphene, especially its selectivity. The results would be important for its extension to a wider range of reactions and for designer technologies involving hydrogen.

Recent progress of heterogeneous catalysts for transfer hydrogenation under the background of carbon neutrality

Under the background of carbon neutrality, the direct conversion of greenhouse CO2 to high value added fuels and chemicals is becoming an important and promising technology. Among them, the generation of liquid C1 products (formic acid and methanol) has made great progress; nevertheless, it encounters the problem of how to use it efficiently to solve the overcapacity issue. In this review, we suggest that the catalytic transfer hydrogenation using formic acid and methanol as the hydrogen sources is a critical and potential route for the substitution for the fossil fuel-derived H2 to generate essential bulk and fine chemicals. We mainly focus on summarizing the recent progress of heterogeneous catalysts in such reactions, including thermal- and photo-catalytic processes. Finally, we also propose some challenges and opportunities for this development.

A Sustainable Approach for Graphene Oxide-supported Metal N-Heterocyclic Carbenes Catalysts

Sustainable noble metal-N-heterocyclic carbenes (NHC's) are a topic of arising concern in both the chemical industry and the academic community due to a growing consciousness of environmental pollution and scarcity. Recovering and reusing homogeneous catalysts from the reaction mixture requires a tremendous amount of capital investment in the chemical manufacturing industry. Heterogeneous catalysts are proved to have better functional groups tolerance; however, catalysts support largely influences the active catalyst sites to affect catalyst efficiency and selectivity. Thus the, choice of catalyst supports plays an almost decisive role in this emerging area of catalysis research. Graphene oxide (GO)/reduced graphene oxide (rGO) support has a potential growth in heterogeneous catalysis owing to their commercial availability, considerably larger surface area, inert towards chemical transformations, and easy surface functionalization to attached metal complexes via covalent and non-covalent aromatic π-conjugates. To take advantage of two independently well-established research areas of noble metal-N-heterocyclic carbenes and GO/rGO support via covalent or non-covalent interactions approach would offer novel heterogeneous complexes with improved catalytic efficiency without sacrificing product selectivity. This unique concept of marrying metal-N-heterocyclic carbenes with GO/rGO support has potential growth in the chemical and pharmaceutical industry, however, limited examples are reported in the literature. In this perspective, a comprehensive summary of metal-NHC synthesis on GO/rGO support and synthetic strategies to graft M-NHC onto GO/rGO surface, catalytic efficiency, for the catalytic transformation are critically reviewed. Furthermore, a plausible mechanism for non-covalent grafting methodology is summarized to direct readers to give a better understanding of M-NHC@rGO complexes. This would also allow the designing of engineered catalysts for unexplored catalytic applications.

Heterogenized Phenanthroline-Pd(2+)-Catalyzed Alkoxycarbonylation of Aryl Iodides in Base-Free Conditions

A phenanthroline-based porous organic polymer-supported heterogeneous Pd catalyst (Pd@Phen-POP) is facilely synthesized by the solvent knitting of a Phen scaffold via the Lewis-acid-catalyzed Friedel-Crafts reaction using dichloromethane as a source for linker in the presence of AlCl₃. The catalyst very effectively catalyzes the alkoxycarbonylation of various substituted aryl iodides with various alcohols to give corresponding products in good to excellent yields. Owing to the heterotic nature of the catalyst, it can be easily separated by simple filtration from the reaction mixture and recycled.

Engineering Nanostructured Interfaces of Hexagonal Boron Nitride-Based Materials for Enhanced Catalysis

ConspectusHexagonal boron nitrides (h-BNs) are attractive two-dimensional (2D) nanomaterials that consist of alternating B and N atoms and layered honeycomb-like structures similar to graphene. They have exhibited unique properties and promising application potentials in the field of energy storage and transformation. Recent advances in utilizing h-BN as a metal-free catalyst in the oxidative dehydrogenation of propane have triggered broad interests in exploring h-BN in catalysis. However, h-BN-based materials as robust nanocatalysts in heterogeneous catalysis are still underexplored because of the limited methodologies capable of affording h-BN with controllable crystallinity, abundant porosity, high purity, and defect engineering, which played important roles in tuning their catalytic performance. In this Account, our recent progress in addressing the above issues will be highlighted, including the synthesis of high-quality h-BN-based nanomaterials via both bottom-up and top-down pathways and their catalytic utilization as metal-free catalysts or as supports to tune the interfacial electronic properties on the metal nanoparticles (NPs). First, we will focus on the large-scale fabrication of h-BN nanosheets (h-BNNSs) with high crystallinity, improved surface area, satisfactory purity, and tunable defects. h-BN derived from the traditional approaches using boron trioxide and urea as the starting materials generally contains carbon/oxygen impurities and has low crystallinity. Several new strategies were developed to address the issues. Using bulk h-BN as the precursor via gas exfoliation in liquid nitrogen, single- or few-layered h-BNNS with abundant defects could be generated. Amorphous h-BN precursors could be converted to h-BN nanosheets with high crystallinity assisted by a magnesium metallic flux via a successive dissolution/precipitation/crystallization procedure. The as-fabricated h-BNNS featured high crystallinity and purity as well as abundant porosity. An ionothermal metathesis procedure was developed using inorganic molten salts (NaNH₂ and NaBH₄) as the precursors. The h-BN scaffolds could be produced on a large scale with high yield, and the as-afforded materials possessed high purity and crystallinity. Second, utilization of the as-prepared h-BN library as metal-free catalysts in dehydrogenation and hydrogenation reactions will be summarized, in which they exhibited enhanced catalytic activity over the counterparts from the previous synthesis method. Third, the interface modulation between metal NPs with the as-prepared defects' abundant h-BN support will be highlighted. The h-BN-based strong metal-support interaction (SMSI) nanocatalysts were constructed without involving reducible metal oxides via the ionothermal procedure we developed by deploying specific inorganic metal salts, acting as robust nanocatalysts in CO oxidation. Under conditions simulated for practical exhaust systems, promising catalytic efficiency together with high thermal stability and sintering resistance was achieved. Across all of these examples, unique insights into structures, defects, and interfaces that emerge from in-depth characterization through microscopy, spectroscopy, and diffraction will be highlighted.

Graphene nano-sieves by femtosecond laser irradiation

The formation of nano-pores in graphene crystal structure is alternative way to engineer its electronic properties, chemical reactivity, and surface interactions, enabling applications in technological fields such as sensing, energy and separation. The past few years, nano-perforation of graphene sheets has been accomplished by a variety of different methods suffering mainly from poor scalability and cost efficiency issues. In this work, we introduce an experimental protocol to engineer nanometer scale pores in CVD graphene membranes under ambient conditions, using low power ultra-short laser pulses and overcoming the drawbacks of other perforation techniques. Using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) we visualized and quantified the nanopore network while Raman spectroscopy is utilized to correlate the nano-perforated area with the nanotopographic imaging. We suggest that Raman imaging provides the identification of nanoporous area and, in combination with AFM, we provide solid evidence for the reproducibility of the method, since under these experimental conditions, nanopores of a certain size distribution are formed.

Tuning low-temperature CO oxidation activities via N-doping on graphene-supported three-coordinated nickle single-atom catalysts

Nitrogen doping is identified as an intriguing way to regulate graphene-supported single-atom catalysts (SACs) for heterogeneous catalysis. However, little theoretical effort has been directed towards exploring the activity trend in terms of N-doping level. In this study, we systematically investigated the N-doping effect on CO oxidation activities for graphene-supported three-coordinated Ni SACs (Ni-N_xC_3-x) in virtue of density functional theory (DFT) calculations and microkinetic modeling. We found that N-doping will shift the d-band center of single-atom Ni upwards, enhance the adsorption of intermediates, and tune the activation barrier to the overall reaction activities. Ni-N₁C₂ exhibits excellent catalytic performance with the highest total reaction rate comparable to that of noble metal SACs. These findings are helpful for understanding the N-doping influence and rationalizing the art of designing novel SACs for CO oxidation at low temperatures.

Effect of the green synthesized rGO and Mg/rGO nanocomposites on the phytochemical assay, toxicity, and metabolism of Mentha longifolia in vitro cultures

Reduced graphene oxide (rGO) and Mg/rGO nanocomposites (NCs) were prepared by an eco-friendly technique using Rosa canina fruit extract. Physicochemical properties and cytotoxicity to Mentha longifolia in vitro cultures of these nanomaterials were examined by using XRD, FESEM, EDX, FT-IR, DLS/zeta potential, UV-Visible, and GC-MS techniques. The characterization techniques confirmed the synthesis of rGO and Mg/rGO NCs with particle sizes less than 20 nm (based on FESEM). In accordance to the biological measurements, rGO showed in vitro cytotoxicity to M. longifolia shoot cultures. Mg/rGO NCs showed no significant difference in the growth parameters except for a decrease in the shoot number at the concentrations of 50 and 150 mg/L and a decrease in the length of the tallest root at the concentrations of 100 and 150 mg/L, however efficiently improved the photosynthetic pigment contents. The phytochemical assay depicted that the total content of volatile compounds was increased in the treated cultures with 25, 50, and 100 mg/L of rGO and Mg/rGO NCs in comparison to the control. Generally, the more oxygenated and hydrocarbon sesquiterpenes were observed in the cultures treated with 25 and 100 mg/L of rGO and 25 and 50 mg/L of Mg/rGO NCs.

Catalytic applications of graphene oxide towards the synthesis of bioactive scaffolds through the formation of carbon–carbon and carbon–heteroatom bonds

During the past several decades, metal-based catalysis is one of the major and direct approaches for the synthesis of organic molecules. Nowadays, materials containing predominantly carbon element which are termed as carbocatalysts, become the most promising area of research to replace transition metal catalysts. In this context of carbocatalysis, the use of graphene oxide (GO) and GO-based materials are under spotlight due to their sustainability, environmental benignity and large scale-availability. The presence of oxygen containing functional groups in GO makes it benign oxidant and slightly acidic catalyst. This chapter provides a broad discussion on graphene oxide (GO) as well as its preparation, properties and vast area of application. The catalytic activity of GO has been explored in different organic transformations and it has been recognized as an oxidation catalyst for various organic reactions.

Pd-Pd/PdO as active sites on intercalated graphene oxide modified by diaminobenzene: fabrication, catalysis properties, synergistic effects, and catalytic mechanism

Pd-Pd/PdO nanoclusters well dispersed on intercalated graphene oxide (GO) (denoted as GO@PPD-Pd) were prepared and characterized. GO@PPD-Pd exhibited high catalytic activity (a TOF value of 60 705 h-1) during the Suzuki coupling reaction, and it could be reused at least 6 times. The real active centre was Pd(200)-Pd(200)/PdO(110, 102). A change in the Pd facets on the surface of PdO was a key factor leading to deactivation, and the aggregation and loss of active centres was also another important reason. The catalytic mechanism involved heterogeneous catalysis, showing that the catalytic processes occurred at the interface, including substrate adsorption, intermediate formation, and product desorption. The real active centres showed enhanced negative charge due to the transfer of electrons from the carrier and ligands, which could effectively promote the oxidative addition reaction, and Pd(200) and the heteroconjugated Pd/PdO interface generated in situ also participated in the coupling process, synergistically boosting activity. Developed GO@PPD-Pd was a viable heterogeneous catalyst that may have practical applications owing to its easy synthesis and stability, and this synergistic approach can be utilized to develop other transition-metal catalysts.

Advances in Graphene/Inorganic Nanoparticle Composites for Catalytic Applications

Graphene-based nanocomposites with inorganic (metal and metal oxide) nanoparticles leads to materials with high catalytic activity for a variety of chemical transformations. Graphene and its derivatives such as graphene oxide, highly reduced graphene oxide, or nitrogen-doped graphene are excellent support materials due to their high surface area, their extended π-system, and variable functionalities for effective chemical interactions to fabricate nanocomposites. The ability to fine-tune the surface composition for desired functionalities enhances the versatility of graphene-based nanocomposites in catalysis. This review summarizes the preparation of graphene/inorganic NPs based nanocomposites and their use in catalytic applications. We discuss the large-scale synthesis of graphene-based nanomaterials. We have also highlighted the interfacial electronic communication between graphene/inorganic nanoparticles and other factors resulting in increased catalytic efficiencies.

An efficient CuO/rGO/TiO2 photocatalyst for the synthesis of benzopyranopyrimidine compounds under visible light irradiation

This study reports the synthesis of CuO/rGO/TiO2 in coupling reaction under visible light irradiation. Its photocatalytic performance was explored in a pseudo 4-component and a domino reaction for the synthesis of benzopyranopyrimidine compounds. It can be recovered and recycled for 5 runs.

Synthesis of a Novel 1D/2D Bi2O2CO3–BiOI Heterostructure and Its Enhanced Photocatalytic Activity

A novel 1D/2D Bi2O2CO3–BiOI heterojunction photocatalyst with high-quality interfaces was synthesized through a hydrothermal method by using Bi2O2CO3 nanorods and KI as raw materials. Two-dimensional (2D) BiOI nanosheets uniformly and vertically grow on the 1D porous Bi2O2CO3 rods. Bi2O2CO3–BiOI heterojunctions exhibit better photocatalytic activity than pure Bi2O2CO3 nanorods and BiOI nanosheets. Cr(VI) (30 mg/L), MO (20 mg/L) and BPA (20 mg/L) can be completely degraded in 8–15 min. The superior photocatalytic performance of 1D/2D Bi2O2CO3–BiOI heterojunction is ascribed to the synergistic effects: (a) vertical 2D on 1D multidimensional structure; (b) the formation of the Bi2O2CO3–BiOI p–n heterojunction; (c) high-quality interfaces between Bi2O2CO3 and BiOI.

Competitive role of nitrogen functionalities of N doped GO and sensitizing effect of Bi2O3 QDs on TiO2 for water remediation

The promising solar irradiated photocatalyst by pairing of bismuth oxide quantum dots (BQDs) doped TiO₂ with nitrogen doped graphene oxide (NGO) nanocomposite (NGO/BQDs-TiO₂) was fabricated. It was used for degradation of organic pollutants like 2,4-dichlorophenol (2,4-DCP) and stable dyes, i.e. Rhodamine B and Congo Red. X-ray diffraction (XRD) profile of NGO showed reduction in oxygenic functional groups and restoring of graphitic crystal structure. The characteristic diffraction peaks of TiO₂ and its composites showed crystalline anatase TiO₂. Morphological images represent spherical shaped TiO₂ evenly covered with BQDs spread on NGO sheet. The surface linkages of NO-O-Ti, C-O-Ti, Bi-O-Ti and vibrational modes are observed by Fourier transform infrared spectroscopy (FTIR) and Raman studies. BQDs and NGO modified TiO₂ results into red shifting in visible region as studied in diffused reflectance spectroscopy (DRS). NGO and BQDs in TiO₂ are linked with defect centers which reduced the recombination of free charge carriers by quenching of photoluminescence (PL) intensities. X-ray photoelectron spectroscopy (XPS) shows that no peak related to C-O in NGO/BQDs-TiO₂ is observed. This indicated that doping of nitrogen into GO has reduced some oxygen functional groups. Nitrogen functionalities in NGO and photosensitizing effect of BQDs in ternary composite have improved photocatalytic activity against organic pollutants. Intermediate byproducts during photo degradation process of 2,4-DCP were studied through high performance liquid chromatography (HPLC). Study of radical scavengers indicated that O₂^·- has significant role for degradation of 2,4-DCP. Our investigations propose that fabricated nanohybrid architecture has potential for degradation of environmental pollutions.

Design of carbon supports for metal-catalyzed acetylene hydrochlorination

For decades, carbons have been the support of choice in acetylene hydrochlorination, a key industrial process for polyvinyl chloride manufacture. However, no unequivocal design criteria could be established to date, due to the complex interplay between the carbon host and the metal nanostructure. Herein, we disentangle the roles of carbon in determining activity and stability of platinum-, ruthenium-, and gold-based hydrochlorination catalysts and derive descriptors for optimal host design, by systematically varying the porous properties and surface functionalization of carbon, while preserving the active metal sites. The acetylene adsorption capacity is identified as central activity descriptor, while the density of acidic oxygen sites determines the coking tendency and thus catalyst stability. With this understanding, a platinum single-atom catalyst is developed with stable catalytic performance under two-fold accelerated deactivation conditions compared to the state-of-the-art system, marking a step ahead towards sustainable PVC production.

Carbons are indispensable as supports for metal-based catalysts in polyvinyl chloride manufacture via acetylene hydrochlorination. In this work, the acetylene interaction, tunable through adjusting microporosity and oxygen sites is identified as central activity and stability descriptor.

Metal-free bifunctional graphene oxide-based carbocatalysts toward reforming biomass from glucose to 5-hydroxymethylfurfural

Graphene oxide (GO) and its derivatives are promising metal-free heterogeneous catalysts due to their high surface area and rich chemical properties. We developed a bifunctional boron-doped sulfonated graphene oxide (BS-GO) and demonstrated its excellent catalytic conversion of glucose to 5-hydroxymethylfurfural (HMF) in a one-pot reaction. BS-GO afforded a high HMF yield of 36.0% from glucose without the use of additives or strong acids. Furthermore, the origin of the catalytic active sites of BS-GO was investigated, unveiling the unique bifunctional catalytic mechanism; it was revealed that two disjunct moieties, boronic acid and phenylsulfonic acid, in a single nanosheet of BS-GO catalyst have a bifunctional effect resulting in excellent catalytic production of HMF. This study suggests the potential of BS-GO as a green and sustainable carbocatalyst for reforming biomass to produce value-added chemicals. We anticipate that the unique structural design presented in this study will provide a guide to afford viable carbocatalysts for diverse organic reactions.

Selectively coupled small Pd nanoparticles on sp2-hybridized domain of graphene-based aerogel with enhanced catalytic activity and stability

The precisely coupling of metal nanoparticles with support domain are crucial to enhance the catalytic activity and stability of supported metal nanoparticle catalysts (MNPs). Here we selectively anchor Pd nanoparticles to the sp² domain in graphene-based aerogel constructed with base-washed graphene oxide (BGO) by removing oxidative debris (OD). The effects of OD on the size and chemical composition of Pd nanoparticles in aerogels are initially unveiled. The removal of OD nanoparticles prompt selective coupling of Pd nanoparticles to the exposed sp²-hybridized domain on BGO nanosheets, and then prevent it from agglomeration. As a result, the Pd nanoparticle size of self-assembled Pd/BGA is 4.67 times smaller than that of traditional Pd/graphene oxide aerogel (Pd/GA). The optimal catalytic activity of Pd/BGA for the model catalytic reduction of 4-nitrophenol is 15 times higher than that of Pd/GA. Pd/BGA could maintain its superior catalytic activity and achieves 98.72% conversion in the fifth cycle. The superior catalytic performance could be ascribed to the small Pd nanoparticles and high percentage of Pd(0) in Pd/BGA, and the enhanced electronic conductivity of Pd/BGA. These integrated merits of Pd/BGA as heterogeneous catalysts are attributed to selectively anchor Pd nanoparticles on sp²-hybridized domain of graphene-based aerogel, and strongly coupled interaction of MNPs with support. The structure-regulated BGO nanosheets could serve as versatile building blocks for fabricating MNPs/graphene aerogels with superior performance for catalytic transformation of water pollutants.

Metallic oxide–graphene composites as a catalyst for gas-phase oxidation of benzyl alcohol to benzaldehyde

A new catalyst (FAG) composed of Fe, Al, and graphene (G) was prepared for catalyzing the reaction of benzyl alcohol (BA) to benzaldehyde (BD). The catalyst was characterized by XRD, XPS, SEM, and BET analyses. The catalytic performance of FAG for oxidation of BA to BD was studied by comparing with the catalysts ferrous oxide (Fe), ferrous oxide doped with aluminum (FA), and ferrous oxide doped with graphene (FG). The effects of amount of graphene additive, temperature, and ratio of Fe and Al were also studied. The results show that the catalyst FAG has a great specific surface area of 80.40 m2 g−1 and an excellent catalytic performance for the reaction of BA to BD: the conversion of BA and yield of BD significantly increased, and the selectivity of BD reached 87.38%.

Practical scale up synthesis of carboxylic acids and their bioisosteres 5-substituted-1H-tetrazoles catalyzed by a graphene oxide-based solid acid carbocatalyst

Herein, catalytic application of a metal-free sulfonic acid functionalized reduced graphene oxide (SA-rGO) material is reported for the synthesis of both carboxylic acids and their bioisosteres, 5-substituted-1H-tetrazoles. SA-rGO as a catalytic material incorporates the intriguing properties of graphene oxide material with additional benefits of highly acidic sites due to sulfonic acid groups. The oxidation of aldehydes to carboxylic acids could be efficiently achieved using H₂O₂ as a green oxidant with high TOF values (9.06-9.89 h^-1). The 5-substituted-1H-tetrazoles could also be effectively synthesized with high TOF values (12.08-16.96 h^-1). The synthesis of 5-substituted-1H-tetrazoles was corroborated by single crystal X-ray analysis and computational calculations of the proposed reaction mechanism which correlated well with experimental findings. Both of the reactions could be performed efficiently at gram scale (10 g) using the SA-rGO catalyst. SA-rGO displays eminent reusability up to eight runs without significant decrease in its productivity. Thus, these features make SA-rGO riveting from an industrial perspective.

Visualization of catalyst dynamics and development of a practical procedure to study complex "cocktail"-type catalytic systems

The ability to distinguish molecular catalysis from nanoscale catalysis provides a key to success in the field of catalyst development, particularly for the transition to sustainable economies. Complex evolution of catalyst precursors, facilitated by dynamic interconversions and leaching, makes the identification of catalytically active forms an important task, which is sometimes very difficult. We propose a simple method for in situ capturing of nanoparticles with carbon-coated grids directly from reaction mixtures. Application of this method to the Mizoroki-Heck reaction allowed visualization of dynamic changes of the dominant form of palladium particles in the reaction mixtures with homogeneous and heterogeneous catalyst precursors. Changes in the size and shape of the palladium particles reflecting the progress of the catalytic chemical reaction were demonstrated. Detailed computational modeling was carried out to confirm the generality of this approach and its feasibility for different catalytic systems. The computational models revealed strong binding of metal particles to the carbon coating comprising efficient binding sites. The approach was tested for trapping Cr, Co, Ag, Ni, Cu, Pd, Cd, Ir, Ru and Rh nanoparticles from solutions containing micromolar starting concentrations of the metal precursors. The developed approach provides a unique tool for studying intrinsic properties of catalytic systems.