Photoreduction Of Graphene Oxide Research Articles

Photo-transformation of graphene oxide in synthetic and natural waters

Graphene oxide (GO) is widely employed due to its outstanding properties, leading to an increasing release into the environment and natural waters. Although some studies have reported on the photo-transformation of GO, its behavior in complex natural waters remains inadequately explored. This study demonstrates that different types of ions may promote the photoreduction of GO in the order of Ca2+ > K+ > NO3− > Na+ by interacting with the functional groups on the surface of GO, and the photoreduction is enhanced with increasing ion concentrations. Additionally, natural organic matter (NOM) can inhibit the photoreduction of GO by scavenging reactive oxygen species. However, with increasing NOM concentrations (≥ 5 mgC/L), more NOM adsorb onto the surface of GO through hydrogen bonding, Lewis acid-base interactions, and π-π interactions, thereby enhancing the photoreduction of GO. On this basis, our results further indicate that the combined effects of different ions, such as Ca2+, Mg2+, NOM, and other complex hydrochemical conditions in different natural waters can promote the photoreduction of GO, resulting in a reduction in oxygen functional groups and the formation of defects. This study provides a theoretical basis for assessing the long-term transformation and fate of GO in natural waters.

On the design and development of foamed GO-hydrogel nanocomposite surfaces by ultra-short laser processing

Graphene oxide (GO) and reduced graphene oxide have outstanding qualities that could be exploited as reinforcement and antibacterial agents in a plethora of biomedical applications. In this contribution, it is reported the deployment of a polyacrylamide GO-hydrogel composite (GO@pAAm) which was photo-converted and structured by ultra-short laser irradiation using a direct laser writing (DLW) approach. The materials were characterized by Fourier Transform Infrared spectroscopy, scanning electron microscopy and confocal microscopy. The laser structure generates a multi-photo-induced effect: surface foaming and patterning, microdomains with enhanced selective water-swelling and effective GO photo-reduction. A first laser scan seems likely to induce the photo-reduction of GO and subsequent laser pulses trigger the structure/foaming. The photo-reduction of GO is evidenced by Raman spectroscopy by the relatively changing intensities of the D to G signals. Macroscopically by an increase in conductivity (decrease in sheet resistance from R S-GO@pAAm = 304 ± 20 kΩ sq−1 to R S-rGO@pAAm-DLW = 27 ± 8 kΩ sq−1) suggesting a reduction of the material measured by 4-Point-Probe.

Identification of Ultraviolet Photoinduced Presolvated Electrons in Water as the Reducing Agent in the Photoreduction of Graphene Oxide

Light-induced reduction of graphene oxide (GO) is a promising and an ingenious way of producing reduced GO (rGO) because it avoids the use of harsh chemicals. However, to date, the physicochemical mechanisms underlying photoreduction remain controversial. For example, there is no consensus on whether GO is reduced in water via direct excitation using ultraviolet (UV) laser light or via radiologically produced solvated electrons. Because of the photoinduced solvated electrons, the excited state of GO exhibits similar electronic absorption responses in the visible and near-infrared (NIR) wavelength range; therefore, distinguishing GO photoreduction dynamics from solvated electron dynamics via transient electronic absorption techniques is challenging. In this work, we used femtosecond-stimulated Raman spectroscopy (FSRS) to understand the ultrafast photoreduction dynamics of GO dispersion in water. Raman pump wavelength was selected to prevent the resonance of the excited-state Raman signal of water while obtaining the fingerprint Raman signals of GO. In contrast to the results of previous studies, our FSRS results indicate that upon UV excitation, the reduction of GO is triggered by the precursor of the solvated electron (presolvated electron) in 300 fs.

Conductive Micropatterns Containing Photoinduced In Situ Reduced Graphene Oxide Prepared by Ultraviolet Photolithography

AbstractHerein, one kind of conductive patterned film with high resolution comprised of reduced graphene oxide (RGO) is prepared by the ultraviolet photolithography technique. RGO working as a conductive filler greatly improves the conductivity of films and is formed through the photoinduced in situ reduction of graphene oxide (GO) added to the photoresist of the patterned films. This photoreduction method is very eco‐friendly and efficient with a reduction time of <20 min. Furthermore, the effect of various factors on the conductivity of the films is investigated in detail, and appropriate conditions are selected to optimize the photoreduction of GO to obtain the best conductivity. The maximum conductivity of the fabricated films is 9.90 S cm−1, and micropatterns can reach 0.98 S cm−1. While photoinduced in situ reduction facilitates the dispersion of RGO in the photoresist, the photoresist also serves as an encapsulant to avoid the contact of RGO with oxygen and moisture in the air, which enables the conductive films and micropatterns to have excellent storage stability and suitability for various substrates, especially flexible substrates. Hence, a feasible strategy is offered for the preparation of conductive films and micropatterns with promising prospects in the field of flexible electronic devices.

Enhancing Free Cyanide Photocatalytic Oxidation by rGO/TiO2 P25 Composites.

Graphene-TiO2 composites have been investigated in various photocatalytic reactions showing successful synergy compared to pristine TiO2. In the present work, graphene oxide (GO) was synthesized by the Hummers method and then reduced graphene oxide-TiO2 composites (rGO/TiO2) were obtained by an in situ GO photoreduction route. X-ray diffraction, FTIR, Raman, UV–vis DRS, and photoluminescence were the main characterization techniques. The obtained composites containing 1 and 3 wt.% rGO were evaluated in the cyanide (50 mg/L) oxidation and Au-cyanide complex (300 mg/L) degradation under UV-A light. The composites showed higher photocatalytic activity than TiO2, mainly with the 1% rGO content. Cyanate and gold nanoparticles, deposited on the photocatalyst’s surface, were the main byproducts during the photocatalyst assessment. The improved photocatalytic activity of the composites was attributed to a higher rate of electron transfer and a lower rate of charge recombination due to the chemical interaction of rGO with TiO2.

Fabrication of reduced graphene oxide with high electrical conductivity by thermal-assisted photoreduction of electrochemically-exfoliated graphene oxide

Electrochemical exfoliation of graphite is a method for synthesizing graphene oxide (GO) with fewer structural defects than GO synthesized by conventional chemical oxidation. Photoreduction of GO has been focused on due to their facile procedures, and environmental friendliness. In this report, electrochemically-exfoliated graphene oxide (EGO) was irradiated by vacuum ultraviolet (VUV) light at 140 °C under a high vacuum environment, named thermal-assisted VUV light treatment. Conductive atomic force microscopy was used to investigate the electrical characteristics of individual sheets on the nanometer scale. The electrical conductivity of the treated sheet (1.4 × 105 S m−1) was higher than the pristine EGO by an order of magnitude. The chemical and structural analysis showed that the EGO was reduced and their π-conjugated domains were restored through a hybrid of photochemical and thermal treatment. These results indicate that our hybrid approach has the potential for reducing the EGO.

In-depth understanding of the photoreduction of graphene oxide to reduced-graphene oxide on TiO2 surface: Statistical analysis of X-ray photoelectron and Raman spectroscopy data

In UV-assisted photoreduction of graphene oxide (GO) using TiO2, TiO2 supplies photogenerated electrons to reduce GO, which exhibits enhanced electrical conductivity, and induce a chemical interaction between TiO2 and reduced-GO (rGO) for improved charge separation. Here, we investigated the photosynthesis of the TiO2–rGO composite with varying the UV irradiation time, TiO2 source (TiO2-D or –HT, commonly employed in dye-sensitized solar cells), and light power. The final products were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and field-emission scanning electron microscopy. Most importantly, the chemical interaction between the rGO matrix and TiO2 was confirmed by X-ray photoelectron spectroscopy (XPS), whereas the carbon defects were studied by Raman spectroscopy. As expected, the chemical interaction between the rGO matrix and TiO2 was confirmed by the formation of Ti–O–C and Ti–C bonds. Moreover, during UV irradiation, the concentration of carbon defects increased evenly, implying that the photodegradation occurred simultaneously with the photoreduction of GO. The XPS and Raman data were further subjected to statistical analyses, including principal component analysis, multivariate linear regression and analysis of variance (ANOVA), and ANOVA–simultaneous component analysis. The results indicated that the irradiation time and TiO2 source had the highest impacts on the final products.

Functionalization and Soft Photoreduction of Graphene Oxide Triggered by the Photoinitiator During Thiol-Ene Radical Addition

Functionalization and Soft Photoreduction of Graphene Oxide Triggered by the Photoinitiator During Thiol-Ene Radical Addition

Direct Laser Writing of Graphene‐Based Electrical Interconnects for Printed Circuit Board Repair

AbstractMalfunctions in printed circuit boards (PCBs) are often caused by damaged copper traces. Printing materials such as metal nanoparticles, conductive polymers, and graphene along with novel printing methods are being actively explored for repairing the conductive connections in PCBs. Because of its high‐resolution capability, direct writing of conductive traces gets significant attention, especially with the widespread use of flexible PCBs. Graphene is an ideal material for such applications due to its excellent electrical and mechanical properties. However, there have been limited reports on graphene‐based methods for the facile fabrication of conductive traces. A novel method of femtosecond laser direct writing of graphene traces by the photoreduction of graphene oxide (GO) to conductive reduced GO (rGO) for repair and modification of legacy PCBs is reported. A trace‐width resolution of 28.4 μm is achieved over a large patterning area of 100 mm × 100 mm. The rGO thickness is found to be tunable from 0.6 to 4.4 μm, while the sheet resistance is minimized to 100 Ω sq−1. The system capability is demonstrated by printing conductive traces on top of a flexible substrate to form a closed path for turning on a light‐emitting diode, as well as, by repairing a commercial PCB.

Free-standing and flexible graphene supercapacitors of high areal capacitance fabricated by laser holography reduction of graphene oxide

Photoreduction of graphene oxide (GO) holds great potential for developing graphene-based electrodes for high-performance supercapacitors (SCs). However, the insufficient micro-nanostructure on photoreduced GO (PRGO) restricts its electrochemical performance. Here, a hierarchically structured PRGO-based planar SC is reported by combining two-beam-laser-interference with the masking technique. The hierarchical structures improve the surface area between PRGO and electrolyte and contribute to format electric double-layer capacitors. Planar device structures with PRGO-based interdigital finger current collectors are beneficial for rapid ion diffusion paths. As a result, the hierarchically structured PRGO-based planar SC achieves an areal capacitance of 3.97 mF cm−2 at 10 mV s−1. The proposed strategy of employing hierarchically structured PRGO in the planar SC design offers a new route for manufacturing high-performance integrated energy storage devices.

Photoreduced nanocomposites of graphene oxide/N-doped carbon dots toward all-carbon memristive synapses

An all-carbon memristive synapse is highly desirable for hardware implementation in future wearable neuromorphic computing systems. Graphene oxide (GO) can exhibit resistive switching (RS) and may be a feasible candidate to achieve this objective. However, the digital-type RS often occurring in GO-based memristors restricts the biorealistic emulation of synaptic functions. Here, an all-carbon memristive synapse with analog-type RS behavior was demonstrated through photoreduction of GO and N-doped carbon quantum dot (NCQD) nanocomposites. Ultraviolet light irradiation induced the local reduction of GO near the NCQDs, therefore forming multiple weak conductive filaments and demonstrating analog RS with a continuous conductance change. This analog RS enabled the close emulation of several essential synaptic plasticity behaviors; more importantly, the high linearity of the conductance change also facilitated the implementation of pattern recognition with high accuracy. Furthermore, the all-carbon memristive synapse can be transferred onto diverse substrates, showing good flexibility and 3D conformality. Memristive potentiation/depression was stably performed at 450 K, indicating the resistance of the synapse to high temperature. The photoreduction method provides a new path for the fabrication of all-carbon memristive synapses, which supports the development of wearable neuromorphic electronics.

New insight into the photo-transformation mechanisms of graphene oxide under UV-A, UV-B and UV-C lights

Photo-transformation dominates the fate of graphene oxide (GO) in the environment. However, the photo-transformation mechanisms of GO under different UV bands remain unclear. Our results showed that UV bands played a crucial role in sunlight-induced GO transformation. UVA and UVB induced significant photo-reduction of GO as indicated by decreasing surface O/C ratio, which could be explained by an O2-independent electron-hole pair-mediated mechanism (Mechanism I), and an O2-dependent reactive oxygen species (ROS)-mediated reduction mechanism (Mechanism II). Mechanism II accounted for 62.7 % and 33.3 % of total GO photo-transformation under UVA and UVB, respectively. Different from UVA and UVB, UVC led to GO reduction under anaerobic condition via Mechanism I and Mechanism III (direct decarboxylation). However, under aerobic condition, UVC caused significant oxidation of GO, which was the combined effect of Mechanisms I-III and the oxidation of graphitic structure on GO with the assistance of O2 (Mechanism IV). Moreover, it was demonstrated that the environmental factors (e.g., dissolved organic matter, phosphate) significantly enhanced the photo-transformation of GO in natural water. The information in the present work is useful for better understanding the fate of GO in aquatic environments.

Photoluminescence Emission during Photoreduction of Graphene Oxide Sheets as Investigated with Single-Molecule Microscopy

Graphene oxide (GO), the oxidized state of graphene, has a similar chemical structure to graphene, except for the existence of many defects and oxygen-containing functional groups. GO could be photoreduced under light irradiation, and it is crucial to study and understand the changes of chemical structure and photoluminescence during this photoreduction process. Herein, by using single-molecule optical microscopy, the photoreduction of three different GO sheets were monitored in situ. The photoluminescence from highly oxidized GO sheets changed continuously under light irradiation, and many blinking spots showed up on this GO sheet surface. The appearance of these blinking events is highly related to the stacking of the GO sheets. Much less blinking could be observed on stacked GO sheets. It was found that the reduction speed of GO in water is much higher than that in air, and much less blinking could be observed when GO was reduced in water. Moreover, this is also highly related to the chemical structures of the GO sheets used for photoreduction. No blinking could be observed on less oxidized GO sheets. This work provides an effective approach for in situ study of the optical properties of GO sheets, boosting a deeper understanding of GO photoreduction. Moreover, this method could also be extended for in situ studying the optical properties of other materials.

In Situ Integration of SERS Sensors for On‐Chip Catalytic Reactions

AbstractThe rapid progress of microfluidics has contributed to modern analytical methodology. However, in situ integration of chemical/biological sensors for on‐chip reaction monitoring remains a big challenge. Herein, reported is the fabrication of an integrated surface‐enhanced Raman scattering (SERS) sensor and graphene‐based catalytic chip by laser scribing of graphene oxide (GO) and Ag nanoparticles (AgNPs) composite (AgNPs@GO). The surface plasmonic effect of AgNPs can promote the photoreduction of GO, inducing a high porous nanostructure. By combining the AgNPs@RGO nanocomposite patterns with polydimethylsiloxane microfluidic channels, a bi‐functional microfluidic chip capable of on‐chip catalysis and SERS detection is fabricated. As a proof‐of‐concept demonstration, on‐chip AgNPs‐catalyzed 4‐nitrophenol (4‐NP) reduction has been implemented, in which the reaction process can be well monitored using the in situ SERS sensor. The integration of SERS sensors with functional microfluidic devices may hold great promise for developing advanced Lab‐on‐a‐Chip systems.

Review of photoreduction and synchronous patterning of graphene oxide toward advanced applications

In view of the bulk production, resolvability, dispersibility of aqueous solution, graphene oxides (GO) prepared by strong chemical oxidation of graphite flakes have been widely used for the production of graphene-like materials. However, because of the insulating nature caused by amounts of defects on its surface, the application of GO material is greatly constrained. Hence, effective reduction of GO becomes critical. The photoreduction of GO showed more attractive properties than conventional thermal/chemical routes due to its synchronous reduction and flexible patterning, which facilitates a number of applications, such as the electrochemical energy storage devices, electronic devices, and biomimetic substrates. In this review, we dedicatedly summarized the latest advances in photoreduction including the fabrications and applied values in multiple fields. We deem that the photoreduction and synchronous patterning of GO will have very prospects in the development of graphene devices.

Laser Fabrication of Graphene-Based Flexible Electronics.

Recent years have witnessed the rise of graphene and its applications in various electronic devices. Specifically, featuring excellent flexibility, transparency, conductivity, and mechanical robustness, graphene has emerged as a versatile material for flexible electronics. In the past decade, facilitated by various laser processing technologies, including the laser-treatment-induced photoreduction of graphene oxides, flexible patterning, hierarchical structuring, heteroatom doping, controllable thinning, etching, and shock of graphene, along with laser-induced graphene on polyimide, graphene has found broad applications in a wide range of electronic devices, such as power generators, supercapacitors, optoelectronic devices, sensors, and actuators. Here, the recent advancements in the laser fabrication of graphene-based flexible electronic devices are comprehensively summarized. The various laser fabrication technologies that have been employed for the preparation, processing, and modification of graphene and its derivatives are reviewed. A thorough overview of typical laser-enabled flexible electronic devices that are based on various graphene sources is presented. With the rapid progress that has been made in the research on graphene preparation methodologies and laser micronanofabrication technologies, graphene-based electronics may soon undergo fast development.

Role of water oxidation in the photoreduction of graphene oxide

By means of a H218O labeling experiment in combination with mass spectrometry tracking, we studied GO photoreduction. Observation of 18O labeled O2 provides direct evidence to confirm that water oxidation occurs during GO photoreduction. In combination with DFT calculations, we propose a mechanism for O2 and CO2 evolution in the photoreduction of GO.

Fabrication of flexible room-temperature NO2 sensors by direct laser writing of In2O3 and graphene oxide composites

In this work, we reported the fabrication of flexible NO2 sensors arrays operating at room temperature on a composite film of In2O3 and graphene oxide (GO) by direct laser writing (DLW) technology. The laser treatment not only induced the photoreduction of GO, leading to a highly porous structure due to the removal of oxygen groups, but also permitted mask-free patterning through a programmable manner, enabling flexible integration of sensor arrays on any substrates. We demonstrated the fabrication of a 2 × 4 NO2 sensors array on a flexible polyimide substrate within 10 min. Our NO2 sensors based on In2O3 and reduced GO (In2O3@RGO) show liner NO2 sensing properties at room temperature, good responsivity and recovery properties, as well as excellent selectivity towards NO2. We deem that the DLW fabrication of flexible NO2 sensorsarrays may contribute to the development of flexible electronics.

A graphene-based sensor for real time monitoring of sun exposure

The photoreduction of graphene oxide (GO) with titanium dioxide (TiO2) was exploited to fabricate a UV sensor for real time monitoring of sun exposure. The sensor was fabricated by simultaneous deposition of GO sheets and TiO2 nanoparticles onto interdigitated electrodes using an AC electrophoresis deposition method. Changes in the resistance of the GO sheets decorated with TiO2 nanoparticles during repeated cycles of exposure to UV were measured to understand the sensitivity of this sensor to UV radiation. Current-time traces revealed that the fabricated UV sensor retains a memory of each cycle of UV exposure; regardless of whether the sensor is exposed to UV for one long cycle or several short cycles. This memory of the extent of UV exposure is a biomimetic approach, analogous to the response of the skin to sun, and means the sensor requires no power except when the data is read from the sensor.

Photo-Reduction of Graphene Oxide by Using Photographic Flash-Light

Photo-Reduction of Graphene Oxide by Using Photographic Flash-Light