Enhanced Thermal Conducting Behavior of Pressurized Graphene-Silver Flake Composites.

Modern electronics continue to shrink down the sizes while becoming more and more powerful. To improve heat dissipation of electronics, fillers used in the semiconductor packaging process need to possess both high electrical and thermal conductivity. Graphene is known to improve thermal conductivity but suffers from van der Waals interactions and thus poor processibility. In this study, we wrapped silver microflakes with graphene sheets, which can enable intercoupling of phonon- and electron-based thermal transport, to improve the thermal conductivity. Using just 1.55 wt % graphene for wrapping can achieve a 2.64-times greater thermal diffusivity (equivalent to 254.196 ± 10.123 W/m·K) over pristine silver flakes. Graphene-wrapped silver flakes minimize the increase of electrical resistivity, which is one-order higher (1.4 × 10-3 Ω·cm) than the pristine flakes (5.7 × 10-4 Ω·cm). Trace contents of wrapped graphene (<1.55 wt %) were found to be enough to bridge the void between Ag flakes, and this enhances the thermal conductivity. Graphene loading at 3.76 wt % (beyond the threshold of 1.55 wt %) results in the significant graphene aggregation that decreases thermal diffusivity to as low as 16% of the pristine Ag filler. This work recognizes that suitable amounts of graphene wrapping can enhance heat dissipation, but too much graphene results in unwanted aggregation that hinders thermal conducting performance.

Invisible Bactericidal Coatings on Generic Surfaces through a Convenient Hand Spray.

Robust antimicrobial coatings featuring high transparency, strong bactericidal activity, and an easy application procedure on generic surfaces can be widely accepted by the public to prevent pandemics. In this work, we demonstrated the hand-sprayer-based approach to deposit complex oxide coatings composed of Co-Mn-Cu-Zn-Ag on screen protectors of smartphones through acidic redox-assisted deposition (ARD). The as-obtained coatings possess high transparency (99.74% transmittance at 550 nm) and long-lasting durability against swiping (for 135 days of average use) or wet cleaning (for a routine of 3 times/day for 33 days). The spray coating enabling 3.14% Escherichia coli viability can further be reduced to 0.21% through a consistent elemental composition achieved via the immersion method. The high intake of Cu2+ in the coating is majorly responsible for the bactericidal activity, and the presence of Ag+ and Zn2+ is necessary to achieve almost complete eradication. The success of extending the bactericidal coatings on other typical hand-touched surfaces (e.g., stainless steel railings, rubber handrails, and plastic switches) in public areas has been demonstrated.

Discontinuity-Enhanced Thin Film Electrocatalytic Oxygen Evolution.

Thin film electrocatalysts allow strong binding and intimate electrical contact with electrodes, rapid mass transfer during reaction, and are generally more durable than powder electrocatalysts, which is particularly beneficial for gas evolution reactions. In this work, using cobalt manganese oxyhydroxide, an oxygen evolution reaction (OER) electrocatalyst that can be grown directly on various electrodes as a model system, it is demonstrated that breaking a continuous film into discontinuous patches can significantly enhance the overall OER performance without sacrificing long-term stability even under elevated electrocatalytic stress. Discontinuous films with higher edge-to-area ratios exhibits reduced overpotentials, increased turnover frequency, and more pronounced current increase after electrochemical conditioning. Operando Raman spectroscopy studies during electrocatalysis reveal that the film edges require lower potential barrier for activation. Introducing discontinuity into thin film electrocatalysis can thus lead to the realization of high performance yet highly robust systems for harsh gas evolution reactions.

Facile and Cost-Efficient Synthesis of Quasi-0D/2D ZnO/MoS2 Nanocomposites for Highly Enhanced Visible-Light-Driven Photocatalytic Degradation of Organic Pollutants and Antibiotics.

Nanoscale transition-metal dichalcogenide materials showed promising potential for visible-light responsive photocatalysis. Here, we report our investigations on the synthesis of heterodimensional nanostructures of two-dimensional (2D) ultrathin MoS2 nanosheets interspersed with ZnO nanoparticles by using a facile two-step method consisting of sonication-aided exfoliation technique followed by a wet chemical process. The photocatalytic activity of the nanocomposites was examined by studying the degradation of different organic dye pollutants and tetracycline, a common antibiotic, under visible-light irradiation. It is found that within 30 min more than 90 % of the model organic dye was photodegraded by the optimized quasi-0D/2D hybrid nanomaterial. The reaction rate of pollutant degradation is about five and eight times higher than those of the pristine MoS2 naonosheets and P25 photocatalysts, respectively. The outstanding photocatalytic activity of the heterodimensional hybrids can be attributed to a few beneficial features from the synergetic effects. Most importantly, the intimate junction between ZnO and MoS2 facilitates the separation of photogenerated carriers, leading to the enhancement of photocatalytic efficiency. A tentative photocatalytic degradation mechanism was proposed and tested. Overall, the present work provides valuable insights for the exploration of cost-effective nanoscale heterodimensional hybrids constructed from atomically thin layered materials.

Narrowband silicon waveguide Bragg reflector achieved by highly ordered graphene oxide gratings.

Graphene oxide (GO) ultrathin film can be wafer-scale deposited by spin coating, can be patterned by laser interference lithography and oxygen plasma etching, can be thinned atomically (0.26 nm/min) and oxidized by ozone treatment, and is a relatively transparent and low-refractive-index material compared to pristine graphene. All those unique properties prompt us to realize a low-loss (∼5 dB/cm), high-extinction-ratio (19 dB), and narrowband (0.425 nm) GO/silicon hybrid waveguide Bragg reflector by transferring 7-nm-thick GO gratings (n=1.58) atop a silicon strip waveguide. Unlike a sidewall-corrugated strip waveguide Bragg reflector that generally exhibits distorted corrugation profiles and is sensitive to fabrication errors, the as-realized GO-grating-covered strip waveguide Bragg reflector exhibits a stable reflecting wavelength and controllable reflection bandwidth that can be well predicted by numerical simulations.

Enhanced Photocatalytic Performance of ZnO Nanorods Coupled by Two-Dimensional α-MoO3 Nanoflakes under UV and Visible Light Irradiation.

We exploit the utilization of two-dimensional (2D) molybdenum oxide nanoflakes as a co-catalyst for ZnO nanorods (NRs) to enhance their photocatalytic performance. The 2D nanoflakes of orthorhombic α-MoO3 were synthesized through a sonication-aided exfoliation technique. The 2D MoO3 nanoflakes can be further converted to substoichiometric quasi-metallic MoO3-x by using UV irradiation. Subsequently, 1D-2D MoO3 /ZnO NR and MoO3-x /ZnO NR composite photocatalysts have been successfully synthesized. The photocatalytic performances of the novel nanosystems in the decomposition of methylene blue are studied by using UV- and visible-illumination setup. The incorporated 2D nanoflakes show a positive influence on the photocatalytic activity of the ZnO. The obtained rate constant values follow the order of pristine ZnO NR

Full Solution-Processed Synthesis and Mechanisms of a Recyclable and Bifunctional Au/ZnO Plasmonic Platform for Enhanced UV/Vis Photocatalysis and Optical Properties.

The synthesis of noble metal/semiconductor hybrid nanostructures for enhanced catalytic or superior optical properties has attracted a lot of attention in recent years. In this study, a facile and all-solution-processed synthetic route was employed to demonstrate an Au/ZnO platform with plasmonic-enhanced UV/Vis catalytic properties while retaining strengthened luminescent properties. The visible-light response of photocatalysis is supported by localized surface plasmon resonance (LSPR) excitations while the enhanced performance under UV is aided by charge separation and strong absorption. The enhancement in optical properties is mainly due to local field enhancement effect and coupling between exciton and LSPR. Luminescent characteristics are investigated and discussed in detail. Recyclability tests showed that the Au/ZnO substrate is reusable by cleaning and has a long shelf life. Our result suggests that plasmonic enhancement of photocatalytic performance is not necessarily a trade-off for enhanced near-band-edge emission in Au/ZnO. This approach may give rise to a new class of versatile platforms for use in novel multifunctional and integrated devices.

Structural Distortion of Molybdenum-Doped Manganese Oxide Octahedral Molecular Sieves for Enhanced Catalytic Performance.

Due to the excellent catalytic performance of manganese oxide (K-OMS-2) in a wide range of applications, incorporation of various dopants has been commonly applied for K-OMS-2 to acquire additional functionality or activities. However, the understanding of its substitution mechanism with respect to the catalytic performance of doped K-OMS-2 materials remains unclear. Here we present the structural distortion (from tetragonal to monoclinic cell) and morphological evolution in K-OMS-2 materials by doping hexavalent molybdenum. With a Mo-to-Mn ratio of 1:20 (R-1:20) in the preparation, the resultant monoclinic K-OMS-2 shows a small equidimensional particle size (∼15 nm), a high surface area of 213 m(2) g(-1), and greatly improved catalytic activity toward CO oxidation with lower onset temperatures (40 °C) than that of pristine K-OMS-2 (above 130 °C). HR-TEM analyses reveal direct evidence of structural distortion on the cross-section of 2 × 2 tunnels with the absence of 4-fold rotation symmetry expected for a tetragonal cell, which are indexed using a monoclinic cell. Our results suggest that substitution of Mo(6+) for Mn(3+) (rather than Mn(4+)) coupled with the vacancy generation results in a distorted structure and unique morphology. The weakened Mn-O bonds and Mn vacancies associated with the structural distortion may be mainly responsible for the enhanced catalytic activity of monoclinic K-OMS-2 instead of dopant species.

Roll-to-Roll Production of Electrocatalysts Achieving High-Current Alkaline Water Splitting.

Scalable production of electrocatalysts capable of performing high-current water splitting is crucial to support green energy utilization. We adopted acidic redox-assisted deposition (ARD) to realize the continuous roll-to-roll fabrication of a strongly adherent cobalt manganese oxyhydroxide (CMOH) film on Ni foam under ambient conditions in water. The as-fabricated products show uniform CMOH coverage and oxygen evolution activities with dimensions as large as 5 m length by 0.25 m width. Also, we converted CMOH into a metallic form (denoted as CM) with the preserved high adhesion to serve as a high-current hydrogen evolution electrocatalyst. Our results reveal that the insufficient adhesion of powder forms electrocatalysts (i.e., Pt and RuO2 as benchmarks), even with the binder, at high-current electrolysis (>1000 mA) can be solved using the fabricated CM||CMOH cell. With an active area of 1 cm × 1 cm assembly in anion exchange membrane (AEM) electrolyzers, we observed the remarkable record of alkaline electrolysis stably at 5000 mA. This result established a new benchmark record on the high-current water splitting research.

Site-specific stamping of graphene micro-patterns over large areas using flexible stamps.

Site-specific stamping has the potential of becoming a low-cost, high-throughput method for depositing specific-shaped graphene micro-patterns over large areas on a wide variety of substrates. The use of an approach involving flexible stamps presented here represents an important advance towards reaching that potential. This approach entails lithographic creation (dry etching) of high-quality micro-pillar arrays of highly oriented pyrolytic graphite (HOPG) over large areas. This is followed by embedding the micro-pillar arrays in polydimethylsiloxane (PDMS), and detaching them from the HOPG base. This results in flexible stamps containing embedded HOPG micro-pillar arrays with freshly cleaved stamping surfaces. The flexible HOPG/PDMS stamps are then brought into contact with substrate surfaces to site-specifically stamp graphene or few-layer graphene (FLG) arrays over large areas. The freshly cleaved nature of the micro-pillar surfaces in the flexible stamps, the low elastic modulus of the flexible stamps and the elimination of sidewall deposits on the micro-pillars allow for more uniform stamping, relative to the use of stiff HOPG stamps from earlier studies. This approach has the potential to expand the substrate choice for graphene or FLG stamping to include curved and/or flexible substrates that could have an impact on the burgeoning field of flexible/stretchable electronics.

Laser-Accelerated Mass Transport in Oxygen Reduction Via a Graphene-Supported Silver-Iron Oxide Heterojunction.

Mass-transport acceleration is essential toward enhanced electrocatalytic performance yet rarely recognized under irradiation, because light is usually reported to improve charge transfer. We studied laser-enhanced mass transport through the heterojunction between Ag and semiconductor Fe2O3 situated on graphene for oxygen reduction reaction. Because of the decreased mass-transport resistance by 59% under 405 nm laser irradiation, the current density can be enhanced by 180%, which is also supported by a theoretical calculation. This laser-enhanced mass transport was attributed to local photothermal heating and the near-field local enhancement. Easier desorption of OH- species occurring between the Fe and Ag centers under the laser accelerates the mass-transport centers.

Nanostructured arrays of semiconducting octahedral molecular sieves by pulsed-laser deposition.

Cryptomelane-type manganese oxide (OMS-2) has been widely used to explore the semiconducting and catalytic properties of molecular sieves with mixed-valent frameworks. Selective synthesis of patterned thin films of OMS-2 with hierarchical nanostructures and oriented crystals is challenging owing to difficulties in preserving the mixed valence, porosity and crystalline phase. Here, we report that pulsed-laser ablation of OMS-2 in an oxygen-rich medium produces a three-dimensional nanostructured array of parallel and inclined OMS-2 fibres on bare substrates of (001) single-crystal strontium titanate. Both parallel and inclined OMS-2 fibres elongate along the [001](OMS-2) direction. The parallel fibres interact strongly with the substrate and grow epitaxially along <110>(STO) with lattice misfits of less than 4%, whereas the inclined fibres are oriented with (301) parallel to the substrate surface. The spontaneous orientation of the crystalline OMS-2 domains over the STO surface opens up a new avenue in lattice-engineered synthesis of multilayer materials.

Micro-droplet Trapping and Manipulation: Understanding Aerosol Better for a Healthier Environment.

Understanding the physicochemical properties and heterogeneous processes of aerosols is key not only to elucidate the impacts of aerosols on the atmosphere and humans but also to exploit their further applications, especially for a healthier environment. Experiments that allow for spatially control of single aerosol particles and investigations on the fundamental properties and heterogeneous chemistry at the single-particle level have flourished during the last few decades, and significant breakthroughs in recent years promise better control and novel applications aimed at resolving key issues in aerosol science. Here we propose graphene oxide (GO) aerosols as prototype aerosols containing polycyclic aromatic hydrocarbons, and GO can behave as two-dimensional surfactants which could modify the interfacial properties of aerosols. We describe the techniques of trapping single particles and furthermore the current status of the optical spectroscopy and chemistry of GO. The current applications of these single-particle trapping techniques are summarized and interesting future applications of GO aerosols are discussed.

Cobalt Iron Oxides Prepared by Acidic Redox-Assisted Precipitation: Characterization, Applications, and New Opportunities.

The microscopic homogeneity of mixed metals in a single-phase oxide is a critical issue in improving material performance. Aqueous alkaline precipitation is the most common approach but it has the limits of microscopic inhomogeneity because of intrinsically different precipitation rates between metal cations. Herein, we demonstrate a new preparation of uniformly structural substituted cobalt iron oxides via acidic redox-assisted precipitation (ARP) upon the interaction of CoII and K2FeO4. This low-pH synthesis features the redox process between Co and Fe, presumably through the formation of inner-sphere complexes such as [(H2O)5CoII-O-FeVIO3]. With the nucleation starting from such complexes, one obtains a product with predominantly mixed-metal Co-O-Fe moieties, which improves the electrical conductivity of the product. This work further analyzes how the properties of the product species evolve during the hydrothermal synthesis step in the ARP process. We see that the Co/Fe ratio slowly increases from about 1:1 to a final value of 2:1, but does not reach the expected redox stoichiometry of 3:1. At the same time, the magnetization also increases, reaching a value of 16.9 emu g-1 for the final superparamagnetic product, which is three times higher than the value of monometallic Co3O4 and Fe2O3. The cobalt iron oxide samples obtained from ARP also possess superior oxygen evolution activity (307 mV overpotential at 10 mA cm-2 µg-1) compared to a mixture of Co3O4 and Fe2O3 (422 mV) or pure cobalt oxide (350 mV), highlighting the structure-induced enhancement of the catalytic activity. The difficult synthesis of evenly blended trinary/quaternary metals in a single-oxide phase may become possible in the future via ARP.

Rational design of hetero-dimensional C-ZnO/MoS2 nanocomposite anchored on 3D mesoporous carbon framework towards synergistically enhanced stability and efficient visible-light-driven photocatalytic activity.

For efficient solar energy harvesting, various engineering strategies to strengthen visible-light responsivity of ZnO photocatalyst is under intensive investigation. In this work, a new ternary C-ZnO/MoS2/mesoporous carbon nanocomposite was successfully prepared by a two-step solution-processed synthesis protocol. The ternary composite exhibits a well-interconnected 3D mesoporous microstructure assembled by carbon nanosheets, which is loaded with quasi 0D ZnO nanoparticles and 2D MoS2 nanosheets. The carbonaceous nanocomposites show enhanced visible-light-driven photocatalytic performance and high photo-corrosion resistance. The incorporation of carbon in the hybrid design has manifold benefits that drastically promotes the photoactivity and photostability. The significant enhancement in photodegradation activity of the hybrid catalysts can be ascribed to a few positive synergistic effects, such as increased surface area and active reaction sites, boosted surface charge utilization efficiency, and band-gap lowering. The high porosity of the distinct microstructure raises the dye adsorption within the material. Tailored interface/surface properties enable more effective mass transport and higher separation efficiency of photo-generated carriers. The modulated electronic structure leads to the narrowing of the ZnO optical bandgap. Meanwhile, coupling with carbon prevents ZnO from photo-corrosion. Our approach highlights the roles of carbon as structure directing and stabilizing agents as well as heteroatom in defect engineering for wide band-gap oxide materials. The rational material design of multivariate mixed-dimensional architecture also provides guiding insight for the advancement of heterogeneous photocatalyst materials with superior performance and durability. The presented engineering strategy would be a promising method for the preparation of nanomaterials supported on 3D carbon network with high porosity and visible-light-driven photocatalytic performance.

Efficient One-Step Conversion of a Low-Grade Vegetable Oil to Biodiesel over a Zinc Carboxylate Metal-Organic Framework.

In this study, a metal-organic framework, namely, Zn3(BTC)2 (BTC = 1,3,5-benzenetricaboxylic acid), was solvothermally synthesized and employed as a catalyst for biodiesel production from degummed vegetable oil via a one-step transesterification and esterification reaction. The resulting Zn3(BTC)2 particles exhibit a well-defined triclinic structure with an average size of about 1.2 µm, high specific surface area of 1176 m2/g, and thermal stability up to 300 °C. The response surface methodology-Box-Behnken design (RSM-BBD) was employed to identify the optimal reaction conditions and to model the biodiesel yield in relation to three important parameters, namely, the methanol/oil molar ratio (4:1-8:1), temperature (45-65 °C), and time (1.5-4.5 h). Under the optimized reaction conditions (i.e., 6:1 methanol/oil molar ratio, 65 °C, 4.5 h), the maximum biodiesel yield reached 89.89% in a 1 wt % catalyst, which agreed very well with the quadratic polynomial model's prediction (89.96%). The intrinsic catalytic activity of Zn3(BTC)2, expressed as the turnover frequency, was found to be superior to that of other MOF catalysts applied in the transesterification and esterification reactions. The reusability study showed that the as-synthesized Zn3(BTC)2 catalyst exhibited good stability upon three consecutive reuses without a noticeable decrease in the methyl ester yield (∼4%) and any appreciable metal leaching (<5%). Furthermore, a preliminary technoeconomic analysis showed that the total direct operating cost for the kilogram-scale production of Zn3(BTC)2 is estimated to be US$50, which may sound economically attractive.

Role of carrier-transfer in the optical nonlinearity of graphene/Bi2Te3 heterojunctions.

Two-dimensional (2D) topological insulators (TIs) have attracted a lot of attention owing to their striking optical nonlinearity. However, the ultra-low saturable intensity (SI) of TIs resulting from the bulk conduction band limits their applications, such as in mode-locking solid-state lasers. In this work, through fabricating a graphene/Bi2Te3 heterojunction which combines monolayer graphene and a Bi2Te3 nanoplate, the optical nonlinearities are analyzed. Moreover, the thickness-dependent characteristics are also investigated by varying the thickness of the Bi2Te3 when synthesizing the heterojunctions. Furthermore, with the aid of the estimated junction electron escape time, a model of the photo-excited carrier-transfer mechanism is proposed and used to describe the phenomena of depression of ultra-low saturable absorption (SA) from the Bi2Te3 bulk band. The increased modulation depth of the graphene/Bi2Te3 heterojunction can accordingly be realized in more detail. In addition, a Q-switched solid-state laser operating at 1064 nm with heterojunction saturable absorbers is built up and characterized for validating the proposed model. The laser performance with varied Bi2Te3 thickness, such as pulse duration and repetition rate, agrees quite well with our proposed model. Our work demonstrates the functionality of optical nonlinear engineering by tuning the thickness of the graphene/Bi2Te3 heterojunction and demonstrates its potential for applications.

Green decomposition of organic dyes using octahedral molecular sieve manganese oxide catalysts.

The catalytic degradation of organic dye (methylene blue, MB) has been studied using green oxidation methods (tertiary-butyl hydrogen peroxide, TBHP, as the oxidant with several doped mixed-valent and regular manganese oxide catalysts in water) at room and higher temperatures. These catalysts belong to a class of porous manganese oxides known as octahedral molecular sieves (OMS). The most active catalysts were those of Mo(6+)- and V(5+)-doped OMS. Rates of reaction were found to be first-order with respect to the dye. TBHP has been found to enhance the MB decomposition, whereas H(2)O(2) does not. Reactions were studied at pH 3-11. The optimum pH for these reactions was pH 3. Dye-decomposing activity was proportional to the amount of catalyst used, and a significant increase in catalytic activity was observed with increasing temperature. X-ray diffraction (XRD), energy dispersive spectroscopy (EDX), and thermogravimetric analysis (TGA) studies showed that no changes in the catalyst structure occurred after the dye-degradation reaction. The products as analyzed by electrospray ionization mass spectrometry (ESI-MS) showed that MB was successively decomposed through different intermediate species.

Removal of chlorpheniramine and variations of nitrosamine formation potentials in municipal wastewaters by adsorption onto the GO-Fe3O4.

Chlorpheniramine is a pharmaceutical pollutant and a precursor of carcinogenic nitrosamines during disinfection/oxidation. In our previous study, graphene oxide coated with magnetite (GO-Fe3O4) was capable of removing chlorpheniramine in deionized water by adsorption. This study investigated the removal of chlorpheniramine and its nitrosamine formation potentials (FPs) by adsorption onto magnetic GO-Fe3O4, with respect to the influence by using real municipal wastewaters as the background. In the results, the adsorption performances of chlorpheniramine in wastewaters decreased in the order: GO-Fe3O4 suspension > GO-Fe3O4 particles > activated carbon. Chlorpheniramine adsorptions on GO-Fe3O4 particles and activated carbon were reduced by using real wastewaters as the background, whereas chlorpheniramine adsorption on GO-Fe3O4 suspension was enhanced due to the effects of surface charge on GO-Fe3O4 and ionic strength variation in water. The fittings of adsorption isotherms indicated that the wastewater background reduced the surface heterogeneity of GO-Fe3O4 suspension and improved the adsorption performance. Appreciable removal efficiencies of NDMA and other nitrosamine FPs were observed when GO-Fe3O4 particles were added in real wastewaters. However, when chlorpheniramine was present in wastewaters, chlorpheniramine adsorption and degradation reaction simultaneously occurred on the surface of GO-Fe3O4, increasing NDMA and other nitrosamine FPs in wastewaters after GO-Fe3O4 addition for chlorpheniramine adsorption. The assumption was further demonstrated by observing the NDMA-FP increase during chlorpheniramine adsorption on GO-Fe3O4 in deionized water. GO-Fe3O4 is a potential adsorbent for chlorpheniramine removal. Nevertheless, the low treatment efficiencies at high doses limit its application for nitrosamine FP adsorptions in real wastewaters.

Regenerable Acidity of Graphene Oxide in Promoting Multicomponent Organic Synthesis.

The Brønsted acidity of graphene oxide (GO) materials has shown promising activity in organic synthesis. However, roles and functionality of Lewis acid sites remain elusive. Herein, we reported a carbocatalytic approach utilizing both Brønsted and Lewis acid sites in GOs as heterogeneous promoters in a series of multicomponent synthesis of triazoloquinazolinone compounds. The GOs possessing the highest degree of oxidation, also having the highest amounts of Lewis acid sites, enable optimal yields (up to 95%) under mild and non-toxic reaction conditions (85 °C in EtOH). The results of FT-IR spectroscopy, temperature-programed decomposition mass spectrometry, and X-ray photoelectron spectroscopy identified that the apparent Lewis acidity via basal plane epoxide ring opening, on top of the saturated Brønsted acidic carboxylic groups, is responsible for the enhanced carbocatalytic activities involving Knoevenagel condensation pathway. Recycled GO can be effectively regenerated to reach 97% activity of fresh GO, supporting the recognition of GO as pseudocatalyst in organic synthesis.