In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets-supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis-related properties of graphene and its derivatives, and design rules and synthesis methods of graphene-based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi-junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H2 production, and CO2 reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene-based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.

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Graphene in Photocatalysis: A Review

Graphene quantum dots (GQDs) that are flat 0D nanomaterials have attracted increasing interest because of their exceptional chemicophysical properties and novel applications in energy conversion and storage, electro/photo/chemical catalysis, flexible devices, sensing, display, imaging, and theranostics. The significant advances in the recent years are summarized with comparative and balanced discussion. The differences between GQDs and other nanomaterials, including their nanocarbon cousins, are emphasized, and the unique advantages of GQDs for specific applications are highlighted. The current challenges and outlook of this growing field are also discussed.

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Recent Advances on Graphene Quantum Dots: From Chemistry and Physics to Applications

Graphene quantum dots from chemistry to applications

Nanomaterials for photoelectrochemical water splitting - review

Herein, we summarize recent research developments and progress of carbon dots (CDs), which have been attracting considerable attention as a new type of photoluminescent material. Raw materials, from single carbonaceous compounds to colorful natural substances, for the synthesis of CDs are discussed. A range of diverse synthetic methodologies to achieve better photoluminescence performance and more advanced functions are summarized, and these are basically divided into two classes: top-down and bottom-up. The inspiring properties, mainly including composites, optical properties and cytotoxicity, are listed. In particular, the luminescence mechanism and surface functionalization of the CDs are briefly discussed. Moreover, on the basis of the above, the long-wavelength and multicolor emission properties of CDs and ways to achieve these goals including surface state and size controlled by synthesis strategies, proper precursors, chemical doping and modification, solvatochromic effects and energy transfer are reviewed in detail.

Carbon dots: materials, synthesis, properties and approaches to long-wavelength and multicolor emission

Graphene quantum dot (GQD)-sensitized ZnO nanorods/poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) Schottky junction has been fabricated for visible-blind ultraviolet (UV) photodetector applications. Schottky diode parameters such as ideality factor, effective work function, and series resistance have been studied for GQD-modified and pristine ZnO nanorod-based devices. Under illumination of broadband light of intensity 80 mW/cm2, GQD-sensitized samples showed 11 times higher photocurrent value compared to pristine ZnO at −0.75 V external bias. GQD-modified detector demonstrated maximum photocurrent at UV region (wavelength ∼340 nm) for all reverse bias voltages. ZnO nanorods/polymer Schottky junction UV detectors revealed high external quantum efficiency (EQE) more than 100%. Interestingly, GQD sensitized nanorod-based device demonstrated high EQE value of 13,161% at −1 V bias (wavelength ∼340 nm), which is eight times higher than pristine ZnO NR-based detector. GQD-modified detectors a...

Graphene Quantum Dot-Sensitized ZnO Nanorod/Polymer Schottky Junction UV Detector with Superior External Quantum Efficiency, Detectivity, and Responsivity

Non-enzymatic electrochemical glucose sensors have been fabricated using hydrothermally grown CuO nanorods on fluorine doped tin oxide (FTO) coated glass substrates. The sensing performance has been increased by several times after attaching Au nanoparticles with CuO nanorods. The formation of CuO nanorods and attachment of Au nanoparticles were confirmed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) study. The Au decorated CuO nanorod electrodes demonstrated glucose sensitivity of 2009 μAmM-1 cm-2, in the linear detection range 5 μM to 1.325 mM, with detection limit of 0.17 μM. Such Au decorated sensing electrodes are highly selective and exhibited long-term stability. Non-invasive glucose detection has been demonstrated using human saliva samples. The sensitivity of the sensor for salivary glucose detection was found to be 1740 μAmM-1 cm-2. Our present study demonstrated the promising use of Au decorated CuO NR electrodes for low cost, non-enzymatic, non-invasive diabetes monitoring application.

Non-enzymatic and non-invasive glucose detection using Au nanoparticle decorated CuO nanorods

DMSO modified PEDOT:PSS polymer/ZnO nanorods Schottky junction ultraviolet photodetector: Photoresponse, external quantum efficiency, detectivity, and responsivity augmentation using N doped graphene quantum dots

Advantages of nitrogen-doped graphene quantum dots as a green sensitizer with ZnO nanorod based photoanodes for solar energy conversion

ZnO nanorods have been grown on indium-tin-oxide coated glass substrates by a low cost chemical process Current-voltage characteristics have been studied using ZnO nanorods as photoanode in an electrochemical cell The flat band voltage shift and depletion width of ZnO nanorods/electrolyte interface have been estimated from Mott-Schottky (MS) characteristics The electrochemical impedance measurements have been carried out to study the charge transport mechanism at the semiconductor-electrolyte interface under dark and white light (100 mW/cm2) illumination The doping concentration of nanorods has been extracted from MS plot Photoresponse behavior of ZnO nanorods is found to be enhanced than seed layers with the incident of white light Spectral dependent photovoltage of ZnO nanorods has been carried out using monochromatic light of wavelength 250–600 nm The photopotential recovery time has been estimated for nanorods and seed layers The stability of ZnO nanorods as a photoanode has been investigated

Tanmoy Majumder

Papers

Graphene Quantum Dot-Sensitized ZnO Nanorod/Polymer Schottky Junction UV Detector with Superior External Quantum Efficiency, Detectivity, and Responsivity

Non-enzymatic and non-invasive glucose detection using Au nanoparticle decorated CuO nanorods

DMSO modified PEDOT:PSS polymer/ZnO nanorods Schottky junction ultraviolet photodetector: Photoresponse, external quantum efficiency, detectivity, and responsivity augmentation using N doped graphene quantum dots

Advantages of nitrogen-doped graphene quantum dots as a green sensitizer with ZnO nanorod based photoanodes for solar energy conversion

Photoelectrochemical and photosensing behaviors of hydrothermally grown ZnO nanorods