Copper, silver, and gold-reduced graphene oxide nanocomposite (Cu-rGO, Ag-rGO, and Au-rGO) were fabricated via the hydrothermal method, which shows unique physiochemical properties. Environment friendly electromagnetic radiation was employed to synthesize rGO from GO. The nonlinear optical phenomenon of noble metal decorated rGO is predominantly due to excited state absorption, which arises from surface plasmon resonance and increases in defects at the surface due to Cu, Ag, and Au incorporation. It is found that the third-order nonlinear absorption coefficient was in the order of 10− 10 m/W, with notable enhancements in the third-order properties of Au-rGO compared to other nanocomposites and their respective counterparts. Functionalizing rGO induces defect states ( sp3), increasing NLO response. Cu, Ag, and Au exhibit higher Surface-Enhanced Raman Scattering (SERS) activity due to rGO-induced structural modifications. SERS signals are influenced by dominant signals from Au nanorods. The electronic structures for pure and doped rGO were investigated through Density Functional Theory (DFT). The computed partial density of states (PDOS) confirms the enhancement of the state in Au-doped rGO is due to the charge transference from Au to C 2p orbital. The optical absorption spectra and PDOS reveal the possibility of free carrier absorption enhancement in Au which validates experimentally observed higher two-photon absorption (β) value of Au-doped rGO. The tuning of nonlinear optical and SERS behaviour with variation in the noble metal upon rGO provides an easy way to attain tuneable properties which are exceedingly required in both optoelectronics and photonics applications.

Herein, the present work focuses on the effective counter electrode for dye-sensitized solar cells. The bottom–up approach was adapted to synthesize Mn2O3 nanorods via the hydrothermal method and the reduced graphene oxide was merged with Mn2O3 to prepare a nanocomposite. The prepared nanocomposites were subjected to physio-chemical and morphological characterizations which revealed the crystalline nature of Mn2O3 nanorods. The purity level rGO was characterized using the Raman spectrum and the Fourier transform infrared spectroscopy employed to find the functional groups. The morphological micrographs were visualized using SEM and TEM and the high aspect ratio Mn2O3 nanorods were observed with 5–7 nm and supported by rGO sheets. The electrocatalytic nature and corrosion properties of the counter electrode towards the iodide electrolyte were studied using a symmetrical cell. The as-synthesized nanocomposites were introduced as counter electrodes for DSSC and produced 4.11% of photoconversion efficiency with lower charge transfer resistance. The fabricated DSSC devices were undergone for stability tests for indoor and outdoor atmospheres, the DSSC stability showed 93% and 80% respectively for 150 days.

The presence of tetracycline (TC) has been detected in the human living environment, and its complex structure makes it difficult to degrade. The green and efficient utilization of electroactivated persulfate advanced oxidation technology for the degradation of tetracycline remains a challenge. In this study, N-doped reduced graphene oxide (N-rGO) was prepared using a hydrothermal treatment method with urea as the nitrogen source. Four different mass ratios of graphene oxide (GO) to urea were synthesized, and the optimal mass ratio was determined through degradation experiments of tetracycline. The N-rGO/EC/PMS three-dimensional electrocatalytic system was constructed, and the influence of the experimental data on TC degradation, such as initial pH, PMS dosage and voltage, was determined. Characterization analysis using scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and other methods was conducted. The efficient catalytic ability of N-rGO was demonstrated through the generation of hydrogen peroxide ( H2O2) and consumption of peroxymonosulfate (PMS). The superiority of the three-dimensional (3D) electrochemical advanced oxidation process was proposed by combining different systems. Furthermore, the presence of hydroxyl radicals (.OH), persulfate radicals ( SO4 ·−), and singlet oxygen (1O2) was identified using electron spin resonance (ESR) technology. The utilization of N-rGO as a three-dimensional electrode, coupled with the advantages of PMS activation and electrochemical oxidation processes, is a promising method for treating organic pollutants in wastewater.

The untreated effluent dropping into the environment from various textile industries is a major issue. To solve this problem, development of an efficient catalyst for the degradation of macro dye molecules has attracted extensive attention. This work is mainly focused on the synthesis of nickel–manganese sulfide decorated with rGO nanocomposite (Ni–Mn-S/rGO) as an effective visible photocatalyst for degradation of textile toxic macro molecule dye. A simple hydrothermal method was used to synthesize Ni–Mn-S wrapped with rGO. The prepared composites were characterized using various techniques such as X-ray diffraction (XRD), high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infra-red spectrometer (FTIR), and ultra violet–visible (UV–Vis) spectroscopy. The photocatalytic performance of nickel sulfide (NiS), manganese sulfide (MnS), nickel–manganese sulfide (Ni–Mn-S), and Ni–Mn-S/rGO nanocomposite was assessed by analyzing the removal of acid yellow (AY) and rose bengal (RB) dyes under natural sun light. Among these, the Ni–Mn-S/rGO nanocomposite showed the high photocatalytic degradation efficiency of AY and RB dyes (20 ppm concentration) with efficiency at 96.1 and 93.2%, respectively, within 150-min natural sunlight irradiation. The stability of photocatalyst was confirmed by cycle test; it showed stable degradation efficiency even after five cycles. This work confirms that it is an efficient approach for the dye degradation of textile dyes using sulfide-based Ni–Mn-S/rGO nanocomposite.

Wearable sensors with highly flexible and sensitive characteristics have attracted research interests in the promising field of electronic skin, health monitoring, and soft robotics. However, the developing of high-performance piezoresistive sensor is full of challenges due to the expensive equipment and complex procedures. Herein, we fabricate a reduced graphene oxide/ polyurethane composite sponge (GPCS) pressure sensor combining with dual-templates. The polyurethane (PU) sponge provides an elastic structure as solid template. Meanwhile, air bubbles as gas template are used to uniformly disperse graphene oxide (GO) sheets. The burst of air bubbles in the process of thermal treatment makes GO coating on the surface of PU skeleton, avoiding the aggregation of reduced graphene oxide. Therefore, the GPCS exhibits excellent compressibility and uniform coating structure. As a result, it also possesses high sensitivity (Gauge Factor = 3.00 in the range of 0–10% strain), fast response time (35 ms), and excellent cyclic piezoresistive stability (5000 loading–unloading cycles) when applied in the pressure sensor field. Moreover, the flexible wearable stress–strain sensor assembled by the GPCS can be easily adhered on the surface of human skin and precisely detect human movements such as elbow bending and finger bending. Such low-cost procedure and excellent sensing performance enable GPCS sensor to demonstrate tremendous application potential in the field of advanced wearable devices.

Photoanode optimization is a fascinating technique for enlightening the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). In this present study, V2O5/ ZnO and reduced graphene oxide (rGO)-V2O5/ZnO nanocomposites (NCs) were prepared by the solid-state technique and used as photoanodes for DSSCs. A wet chemical technique was implemented to generate individual V2O5 and ZnO nanoparticles (NPs). The structural characteristics of the as-synthesized NCs were investigated and confirmed using powder X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and Scanning electron microscope (SEM) with energy dispersive X-ray (EDX) analysis. The average crystallite size (D) of the as-synthesized V2O5/ ZnO and rGO-V2O5/ZnO NCs was determined by Debye-Scherer’s formula. The bandgap (eV) energy was calculated from Tauc’s plots, and the bonding nature and detection of the excitation of electrons were investigated using the Ultra violet (UV) visible spectra, Fourier Transform infrared (FTIR) and photoluminescence (PL) spectral analysis. Electrical studies like Hall effect analysis and the Nyquist plots are also described. The V2O5/ ZnO and rGO-V2O5/ZnO NCs based DSSCs exhibited 0.64% and 1.27% of PCE and the short circuit current densities and open circuit voltages improved from 7.10 to 11.28 mA/cm2 and from 0.57 to 0.68 V, respectively.

A simple and one-pot synthetic procedure using two different sources has been demonstrated to prepare heteroatoms doped reduced graphene oxide such as nitrogen-doped reduced graphene oxide (N-RGO) and sulfur-doped reduced graphene oxide (S-RGO). The N-RGO has been hydrothermally synthesized using urea as nitrogen precursor, wherein the S-RGO has been synthesized using dimethyl sulfoxide (DMSO) as sulfur precursor. The successful N-doping, S-doping and other physicochemical properties of N-RGO and S-RGO have been confirmed with different spectroscopic and electrochemical techniques. The results indicated that doping into the graphene structure exhibits a high conductivity and a better transfer of charge. Moreover, heteroatoms doped graphene (N-RGO and S-RGO) and graphene-related materials (RGO) have been applied for the individual detection of uric acid (UA). Interestingly, the N-RGO exhibited a lower limit of detection (LOD, S/N = 3) of 2.7 10– 5 M for UA (10–1000 μM) compared with undoped RGO and S-RGO. Furthermore, the simultaneous detection of UA in the presence of Xanthine (XA) has been demonstrated a wide linear range of detection for UA: 10–1000 μM, with unchanged concentration of XA to be 200 μM, and exhibited a low limit of detection of 8.7 10− 5 M ( S∕N = 3) for UA. This modified sensor based on N-RGO has revealed a high selectivity and reproducibility thanks to its large surface area, high catalytic properties, and chemical structure. Indeed, the practical applicability of the proposed sensor has been evaluated in milk samples even in the presence of high concentrations of UA with satisfactory results.

Flexible supercapacitors (FS) are ideal as power backups for upcoming stretchable electronics due to their high power density and good mechanical compliance. However, lacking technology for FS mass manufacturing is still a significant obstacle. The present study describes a novel method for preparing FS based on reduced graphene oxide (RGO) using the N+ plasma technique, in which N+ reduces graphene oxide on the surface of a cotton/polyester substrate. The effect of aloe vera (AV) as a natural reducing & capping agent and carbon nanotubes (CNT) as nanoconductors on the electrochemical performance of the electrodes is studied. FESEM and XPS were employed to investigate the electrodes' structural and chemical composition of electrodes. The galvanostatic charge–discharge curves of electrodes revealed the enhancement of the electrochemical activity of the as-prepared electrode upon additions of AV and CNT. The areal capacitance of the RGO, RGO/AV, and RGO/ AV/CNT supercapacitors at 5 mV/s was 511, 1244.5, and 1879 mF/cm2, respectively. The RGO electrode showed capacitive retention of 80.9% after 2000 cycles enhanced to 89.7% and 92% for RGO/AV and RGO/AV/CNT electrodes, respectively. The equivalent series resistance of the RGO electrode was 126.28 Ω, decreased to 56.62 and 40.06 Ω for RGO/AV and RGO/ AV/CNT electrodes, respectively.

Magnetically separable and reusable zinc ferrite/reduced graphene oxide ( ZnFe2O4/rGO) nanocomposite has been prepared by hydrothermal method. The results illustrate that the construction of ZnFe2O4 and rGO occur concurrently in a hydrothermal reaction that initiates the formation of rGO-wrapped ZnFe2O4 nanospheres. The morphological and structural features of the ZnFe2O4/ rGO nanocomposites reveal that the rGO nanosheets anchored to the ZnFe2O4 sphere act as a self-protective clamping layer to avoid the photo corrosion effect under photo irradiations. The nanocomposites express the soft magnetic behavior with high saturation magnetization under annealing temperature at 300 °C, which may attribute to the well-defined crystalline structure and surface defects. In addition, the GZF 300 nanocomposites exhibit the enhanced photocatalytic degradation over Rhodamine B dye which is 3.4, 1.15, and 1.32 times higher than that of ZF, GZF, and GZF 600 over under visible irradiation in 120 min. The GZF 300 nanocomposites demonstrate their ability to degrade RhB efficiently, even after several photocatalysis cycles with high catalyst recovery by its magnetically separable behavior. The high densities of oxygen defects improvise electron transfer from ZnFe2O4 to rGO and delay the recombination process of the nanocomposite, resulting in enhanced visible photocatalytic activity. The strong magnetic properties of rGO wrapped ZnFe2O4 nanocomposite catalysts the easy separation from the suspension system for multiple usages in water treatment.

The effect of the laser ablation duration of reduced graphene oxide sheets on their optical properties was studied. After 30 min of ablation, the average lateral size of reduced graphene oxide sheets decreases from 347.4 ± 86.5 nm to 98.8 ± 36.0. The sizes of almost all particles are in the range up to 100 nm, which was confirmed by transmission electron microscopy and dynamic light scattering data. The FTIR spectroscopy data showed that after ablation the intensity of the bands associated with O–H, C–OH and C=O vibrations were noticeably decreased. The optical density and the fluorescence intensity of reduced graphene oxide also depend on the ablation time. After ablation, the reduced graphene oxide fluorescence intensity increased 2–3 times. The fluorescence lifetime decreases both for the first (from 1.36 ns to 0.71 ns) and second (from 6.03 to 3.66 ns) components. A broad band was recorded in the long-lived luminescence spectrum. The long-lived luminescence intensity is higher on 80% for the samples after 30 min of ablation compared to the unablated sample. It was assumed that during laser ablation of reduced graphene oxide a change in the ratio between oxidized and sp2- hybridized carbon occurs. This opens up possibilities for controlling the optical properties of reduced graphene oxide.

As frontier materials, graphene oxide (GO) and graphene have penetrated almost all research areas and advanced numerous technologies in sensing, electronics, energy storage, catalysis, water treatment, advanced composites, biomedical, and more. However, the affordable large-scale synthesis of high-quality GO and graphene remains a significant challenge that negatively affects its commercialisation. In this article, firstly, a simple, scalable approach was demonstrated to synthesise high-quality, high yield GO by modifying the improved Hummers method. The advantages of the optimised process are reduced oxidation time, straightforward washing steps without using coagulation step, reduction in cost as eliminating the use of phosphoric acid, use of minimum chemical reagents, and increased production of GO per batch (~ 62 g). Subsequently, the produced GO was reduced to reduced graphene oxide (rGO) using three different approaches: green reduction using ascorbic acid, hydrothermal and thermal reduction techniques. The GO and rGO samples were characterised using various microscopy and spectroscopy techniques such as XRD, Raman, SEM, TEM, XPS and TGA. The rGO prepared using different methods were compared thoroughly, and it was noticed that rGO produced by ascorbic acid reduction has high quality and high yield. Furthermore, surface (surface wettability, zeta potential and surface area) and electrical properties of GO and different rGO were evaluated. The presented synthesis processes might be potentially scaled up for large-scale production of GO and rGO.

Cerium oxide decorated on nickel hydroxide anchored on reduced graphene oxide (Ce-Ni(OH)2/rGO) composite with hexagonal structures were synthesized by facile hydrothermal method. Fourier transform infrared spectroscopy (FT-IR), highresolution transmission electron microscopy with selected area diffraction (HRTEM-SAED), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer– Emmett–Teller (BET) surface area analysis and electrochemical technology were used to characterize the composite. Due to its unique two-dimensional structures and synergistic effect among Ce2O3, Ni(OH)2 and rGO components indicated twodimensional hexagonal nano Ce-Ni(OH)2/rGO composite is promising electrode material for improved electrochemical H2O2 sensing application. From 50 to 800 μM, the H2O2 concentration was linearly proportional to the oxidation current, with a lower detection of limit of 10.5 μM (S/N = 3). The sensor has a higher sensitivity of 0.625 μA μM−1 cm− 2. In addition, the sensor demonstrated high selectivity, repeatability and stability. These findings proved the viability of the synthetic method and the potential of the composites as a H2O2 sensing option.

The reduced graphene oxide (rGO) has attracted more and more attention in recent years. How to choose a suitable reduction method to prepare rGO is a critical problem in the preparation of graphene composites. In this work, the differences of rGO reduced by thermal, microwave, Ultraviolet (UV) and reducing agent were studied. The reduction degree and functional groups of rGO were compared by SEM, XPS, Raman, FTIR and TGA. Thermal can remove most of the oxygen-containing groups of graphene oxide (GO) and the thermal reduction is the most effective reduction method. UV light can directly act on the unstable oxygen-containing groups, and its reduction efficiency is second only to thermal reduction. The efficiency of chemical reduction is not as good as that of UV reduction, because the reducing agent only act on the surface of GO. Microwave reduction is a mild thermal reduction with the lowest efficiency, but the residual oxygen-containing groups increase the hydrophilicity of rGO. To sum up, this work studies that rGO prepared by different reduction methods has different characteristics, which provides a reference for selecting appropriate reduction methods to prepare graphene composites with better properties.

Graphene-based materials show excellent properties in various applications because of their electrical properties, large surface areas, and high tolerance for chemical modification. The use of wet-process is a promising way for their mass production. Heteroatom doping is one of the common methods to improve their electrical, physical, and electrochemical properties. In this work, we develop a new route for the production B-doped graphene-based materials using low-temperature wet-process, which is the reaction between graphene oxide suspensions and a BH3 adduct in tetrahydrofuran under reflux. Elemental mapping images show well-dispersed B atoms along the materials. Various spectroscopic characterizations confirm the reduction of the graphene oxide and incorporation of B atoms into the carbon network as high as ~ 2 at%. The materials showed electrocatalytic activity for oxygen reduction reactions.

Most recently, graphene-related composite-modified electrode surfaces are been widely employed to improve surface interactions and electron transfer kinetics. Hydrothermally prepared strontium pyro niobate (SPN) and reduced graphene oxide/ strontium pyro niobate (RGOSPN) nanostructures reveal excellent morphology. X-ray diffraction analysis of SPN and RGOSPN agree with standard data. Thermogravimetry–differential scanning calorimetry analyses show that RGOSPN has higher thermal stability than SPN. In addition, from the polarization–electric field (P–E) loop measurements, the estimated value of remnant polarization (Pr) and coercive electric field (Ec) of SPN are 0.039 μC cm−2 and − 2.90 kV cm−1 and that of RGOSPN nanocomposite are 0.0139 μC cm−2 and − 2.04 kV cm−1. Cyclic voltammetry measurements show that RGOSPN nanocomposite manifests the possibility of electrochemical reversibility beyond long cycles without change in performance. The redox cycle reveal that RGOSPN can be used as part of a composite electrode for hybrid capacitors dynamic conditions. Moreover, the specific capacitance of SPN and RGOSPN was calculated using galvanostatic charge–discharge (GCD) technique. The observed energy density of 9.1 W h kg−1 in RGOSPN is higher when compared with previous reported values.

Here, Zn ferrite is synthesized along with reduced graphene oxide (rGO) by a facile one-step hydrothermal method. The difference between the synthesized nanocomposites with those in other reported work is that the reaction conditions in this work are 160 oC for 12 h. The synthesized products are characterized by field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and attenuated total reflection. Further, the adsorption property of rGO–Zn ferrite (rGZF) nanocomposite is studied after confirming its successful synthesis. The adsorption capacity of rGZFs toward rhodamine B (RB) is ˃ 9.3 mg/g, whereas that of bare ZF nanoparticles is 1.8 mg/g in aqueous media. The efficiencies of rGZF and bare ZF to remove RB are 99 % and 20 %, respectively. Employing rGZF, 60 % of RB is decomposed within 5 min. The kinetic study reveals that the adsorption process of removing RB by bare Zn ferrite follows pseudo-firstorder kinetics. However, after zinc ferrite is incorporated with rGO, the kinetics changes to pseudo-second-order. Furthermore, the Langmuir isotherm is accomplished by the adsorption process employing rGZF, indicating that a monolayer adsorption process occurs. The thermodynamic parameters of the process are also calculated.

Polypyrrole (PPy) decorated on reduced graphene oxide (rGO) films is successfully prepared with pyrrole (Py) monomers and rGO through one-step combining oxidation with polymerization reaction. Compared with the pure individual components, rGO/PPy compound turns out better electrochemical characteristics owing to the introduction of rGO sheets, which improves the specific surface area and the conductivity of composite material. When the amount of rGO is 10% of the total, the rGO/PPy compound delivers the best capacitance of 389.3 F g−1 at 1.0 A g−1 in a three-electrode system and 266.8 F g−1 at 0.25 A g−1 in the symmetric supercapacitor system. In addition, asymmetric device (rGO/PPy//AC) has been successfully fabricated using optimized rGO/PPy compound as positive electrode, activated carbon as negative electrode (AC) and 1 M Na2SO4 aqueous solution as electrolyte. The device obtains long cycle stability under the high-voltage region from 0 to 1.6 V, meanwhile displaying the satisfied energy density of 19.7 Wh kg−1 at 478.1 W kg−1. Besides, the rGO/PPy//AC device presents satisfactory rate capability and long life time.

The reduced graphene oxide (rGO)/activated carbon (AC) composites are coated on the aluminum substrate using spray coating technique to fabricate nanocarbon-based supercapacitor. Polymer-based solid-state xanthan-gum/Na2SO4 electrolyte is also introduced to increase stability of the supercapacitor. The electrochemical properties of the supercapacitor are evaluated using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge tests. The highest capacitance value of the rGO/AC composite-based supercapacitor is 120 F/g. The rGO/AC composite-based supercapacitor has also retained ~ 85% of its initial capacitance value after 3000 galvanostatic charge/discharge cycles.