Applied Bias Potential Research Articles

Optical and mass spectral characterization of the electrospray ionization/corona discharge ionization interface

The interchange between electrospray ionization (ESI) and corona discharge ionization (CDI) with respect to applied bias on the needle is customarily placed at the point where light production begins at the tip of the needle. If a liquid sample is flowing through a needle that is observed to produce light, the ionization process is assumed to be harsher and the term coronaspray ionization has been coined to describe this hybrid ionization mechanism. In this work, the transition between ESI and CDI is investigated with respect to applied bias through optical and mass spectrometric measurements. As a function of applied bias potential, the optical signal at the tip of the needle was recorded simultaneously with the resultant ionization products. In this effort, the production of ions from an electrospray ionization needle has been demonstrated to produce light regardless of bias if ions are also formed. With this understanding, an ESI/CDI needle was designed to allow the bias to be temporarily pulsed over the ‘onset’ voltage necessary for ionization and the rise and decay of the optical signal was measured. Positive mode CDI onset to a stable discharge state within 0.05 ms, while positive ESI required 1.9 ms to reach a stable condition. In the negative mode, the stability of the ionization process was highly variable in both ESI and CDI modes, though CDI was generally faster to reach the stable mode of operation. When the resultant ions were investigated, the effect of increased bias on an ESI needle was found to be species-dependent. Recognizing that the range of compounds probed was limited, for those examined, it appears that stable, non-labile species may be investigated via ESI under extremely high biases while labile species demonstrate a narrow range of stable biases before significant fragmentation occurs.

Effective Temperatures of Olivine Dust Impact Plasmas

The effective temperatures of the positive and negative charge carriers in impact plasma are measured experimentally. The measurements are performed using a dust accelerator using polypyrrole (PPy)-coated olivine dust particles impacting onto a tungsten (W) target in four velocity bins: 2–3.6, 5–6.6, 8–12, and 12–18 km/s. The setup measures the retained impact charge as a function of applied bias potential, and the temperatures are calculated by fitting the data. The effective temperatures of the cations are approximately 7 eV and independent of the impact speed. The effective temperature of the negative charge carriers changes from 1 eV for the lowest speed to values comparable to that of the cations at higher speeds. The temperature measurements presented here are significantly different from prior studies using Fe dust particles. The discrepancy is possibly due to a larger fraction of negative ions in the impact plasma that likely originates from the PPy coating.

Ti-Based Solid-State Imprinted-Cu2O/CuInSe2 Heterojunction Photoelectrochemical platform for Highly Selective Dopamine Monitoring

An innovative method is developed based on a surface functional photoactive monomer-directing assay for the design of an ultrasensitive and selective molecularly imprinted polymer (MIP) grown on a semiconductor heterojunction for photoelectrochemical dopamine recognition. A dopamine-imprinted poly-orto-phenylenediamine (P-o-PDA) coated on Ti foil electrode is modified with a new double photosystem type II heterojunction formed by coupling dendrite-like CuInSe2(CIS) with Cu2O nanoparticles. It was prepared by electropolymerization, which provided high capacity and fast kinetics to monitor dopamine as biomarker. o-PDA acts as a signal indicator and a functional monomer for MIP. In addition, Cu2O/CIS acts as photoelectric convertor and amplifier layer for PEC-sensing. Under visible light irradiation, the MIP-CIS/Cu2O-coated Ti foil exhibited admirable cathodic photocurrent response, owing to the p-type properties of CIS/Cu2O heterojunction, where signal quenching was obtained in the presence of dopamine due to hindrance effect. Influence of factors including pH, light wavelength and applied bias potential on the PEC response toward dopamine was optimized and the MIP-CIS/Cu2O-based PEC sensing system exhibited satisfying responses toward target dopamine within two working range from 0.1-5.5 μM and 5.5-150 μM at a low detection limit of 2.1 nM. The PEC sensor designed with high photo-electron conversion efficiency showed good stability, high reproducibility, repeatability and selectivity. Its feasibility for potential applications was also illustrated in the analysis of real samples, providing a novel way for the logical design of organic-inorganic heterojunction-based PEC sensors to detect biomarkers.

Boosting the visible-light photoelectrochemical performance of C3N4 by coupling with TiO2 and carbon nanotubes: An organic/inorganic hybrid photocatalyst nanocomposite for photoelectrochemical water spitting

Developing photoanode with proficient sunlight harvesting, stability as well as enhancing the electron injection across the interface remains a major challenge in the photoelectrochemical water splitting strategy to generate hydrogen. Herein, we design and fabricate an organic/inorganic TiO2/C3N4/CNT photoanode by a hydrothermal technique which exhibits much enhanced photoelectrochemical properties. The TiO2/C3N4/CNT photoanode exhibits a photocurrent density of 2.94 mA/cm2, which is ~6.4 time higher than pristine graphitic carbon nitride (C3N4) at an applied bias potential of 0.6 V vs. Ag/AgCl. The excellent photoelectrochemical performance benefits from the impactful migration of photo-induced electrons at the TiO2/C3N4 interface from C3N4 to TiO2 and their intimate interface contact with CNT. Kelvin probe force microscopy result shows a smaller interface barrier height (~10 meV) between TiO2 and C3N4, suggesting that electrons transport is favored through TiO2/C3N4 interfaces in a ternary photoanode. The TiO2/C3N4/CNT photoanode exhibited an onset potential of 0.25 V vs. Ag/AgCl which is much lower compared to pristine C3N4. The electrochemical impedance spectroscopy results also confirmed the enhanced electron injection across the interface in a ternary photoanode. These results demonstrate a promising approach to develop a highly proficient and visible light active photoanode with excellent stability for renewable energy applications.

High-valent ruthenium(IV)-oxo complex stabilized mesoporous carbon (graphitized)/nafion modified electrocatalyst for methanol oxidation reaction in neutral pH

Abstract Owing to its importance in the fuel cell, biofuel and bioinorganic chemistry, since 1981, there has been an immense interest in the development of surface-confined ruthenium-oxo complex and to utilize it as a model bio-mimicking system for oxidation of water and alcohol reactions. In this connection, ruthenium-oxo complex has been attached on solid-surfaces by various chemical approaches. Indeed, the preparation of stable and fouling-free surface-confined ruthenium-complex system is a challenging task. Herein, we report a new methodology based on a modification of [Ru(tpy)(DMSO)Cl2]-Nafion (Nf) precursor, wherein, tpy = 2,2′:6′,2″-terpyridine ligand, system on a graphitized mesoporous carbon (GMC) modified electrode followed by electrochemical treatment for in-situ conversion to a high-valent ruthenium oxo complex electrode, designated as GCE/GMC@[(tpy)RuIV/III=O]-Nf, in pH 7 phosphate buffer solution. It showed a stable and well-defined redox peak at a standard electrode potential, Eo’ = 0.780 V vs Ag/AgCl with a surface-excess value, 5.5 × 10−9 mol.cm−2. Some of the kinetic parameters such as transfer coefficient, α and heterogeneous electron-transfer rate constant, ks values were evaluated as 0.54 and 2.43 s−1 respectively for the redox couple. Collective physicochemical characterizations of the surface-confined system by TEM, Raman, UV–Vis and FTIR spectroscopic techniques and ESI-MS analysis, it has been revealed that [RuIII(tpy)(DMSO)(Cl)(OH)]+ complex is surface-confined on the electrode via π-π interaction, pore-encapsulation, and ionic interaction and further transformed to [(tpy)(DMSO)RuIVO]2+ like complex at an applied bias potential, 0.8 V vs Ag/AgCl. This new surface-confined electrode showed high efficient and enzyme-free electrocatalytic oxidation of methanol with a current sensitivity of 39 μA mM−1 in a neutral pH solution.

Hydrothermal Growth of Molybdenum Disulfide Composited with Electrodeposited Gold and Its Photoelectrochemical Properties

Recently, molybdenum disulfide (MoS2) has received remarkably attention due to its excellent optical and electrical properties. Notably, the narrow bandgap of transition metal dichalcogenide (TMDC) MoS2 makes it a promising candidate for photoelectrochemical (PEC) applications. Direct growth of MoS2 via hydrothermal synthesize offers improved electrical conductivity between the MoS2 and the substrate, which allows for better application and electrical signal readings as a result of elevated electron transfer routs compared with drop-casted MoS2. Here, we studied the effect of hydrothermal growth time of MoS2 nanosheets on the morphology evolution as well as the PEC sensing properties. The time evolution studies conducted in the range of 2-10 hours. We used surface characterization method such as field emission scanning electron microscopy and analytical techniques such as chronoamperometry, cyclic voltammetry and electrochemical impedance spectroscopy to study the morphology evolution and PEC sensing properties. Our results revealed that the direct growth of MoS2 not only enhances the sensor signal but also encourages nanocomposites of MoS2 with gold- a key to simultaneouse amplification of the optical and electrical properties. Effect of applied bias potential in the range of 0.45-0.85 V vs. Ag/AgCl on photocurrent response was also investigated. We further used 3D COMSOL simulation to assess the effect of gold thickness on the electric field intensity of the sensing MoS2/Au electrodes. Eventually, we studied sensitive and selective detection of glucose as an important molecule in the human body. Our developed MoS2/Au composite demonstrated a very low limit of detection (1.3 nM) and excellent sensitivity for non-enzymatic PEC sensing of glucose. Moreover, the selectivity of the fabricated sensor were examined by monitoring the photocurrent responses towards different interfering agents under illumination.

An efficient g-C3N4-decorated CdS-nanoparticle-doped Fe3O4 hybrid catalyst for an enhanced H2 evolution through photoelectrochemical water splitting

We developed a highly efficient and stable g-C3N4-decorated CdS-nanoparticle-doped Fe3O4 nanocube catalyst, g-C3N4@CdS–Fe3O4 (gCNCSF), with a two-step solvo-thermal process in an aqueous phase. It enhanced H2 evolution via photoelectrochemical (PEC) water splitting. Melamine and isolated onion leaf extract were used to prepare g-C3N4 by calcination under an N2 atmosphere at 450 °C. Subsequently, a CdS@Fe3O4 catalyst was fabricated by doping CdS nanoparticles into the interfacial layers of Fe3O4, via a hydrothermal method, following calcination at 450 °C under N2. According to the PEC analysis, the gCNCSF catalyst exhibited a photo-current density of 0.023 mA/cm2, approximately 2.5 and 6.25 times higher than those of binary hybrids g-C3N4@CdS and CdS@Fe3O4, respectively. In addition, approximately 4.1 and 27.7 times higher performance has been recorded than those of neat CdS and g-C3N4, respectively. This was at an applied bias potential of 0.2 V vs. Ag/AgCl. The high rate of H2 evolution could be attributed to the interfacial coordination between g-C3N4 and CdS nanoparticles doped in the Fe3O4 nanocubes, which eventually promoted the bandgap-dependent interfacial charge transfer.

Improved photocurrent generation of three hybrid films made of [BW11Co(H2O)O39]7- and hemicyanines with alkyl linkers of varying length

A series of electrostatically self-assembled films consisting of a Keggin-type cobalt-substituted tungstoborate anion [BW11Co(H2O)O39]7- (BW11Co) and three hemicyanine cations with two chromophores linked by varying lengths of alkyl chains, (E)-1,1'-(propane-1,3-diyl)bis(4-(4-(dimethylamino)styryl)pyridinium) cation (H3), (E)-1,1'-(hexane-1,6-diyl)bis(4-(4-(dimethylamino)styryl)pyridinium) cation (H6), and (E)-1,1'-(decane-1,10-diyl)bis(4-(4-(dimethylamino)styryl)pyridinium) cation (H10), were successfully prepared by layer-by-layer self-assembly technique. UV–visible spectra showed that BW11Co and Ha (a = 3, 6, 10) components were uniformly deposited in each dipping cycle. The visible absorption peaks of (BW11Co/Ha)n films are obviously red shifted as compared with those of corresponding Ha solution, which is beneficial for improving photoelectric conversion. As irradiated with white light, the (BW11Co/Ha)n films generated stable, large cathodic photocurrents that increasing with increasing negative applied bias potentials, increasing of electron acceptor concentrations and decreasing electron donor concentrations in the electrolyte solution. The photocurrents were also found to be strongly depending on layer number of the films, and alkyl chain length in the hemicyanine dyes of Ha (a = 3, 6, 10). The maximum photocurrent densities generated by (BW11Co/H3)4, (BW11Co/H6)5, and (BW11Co/H10)4 films were found to be 18.05, 16.6 and 15.8 μA/cm2, respectively. The photocurrent generation performance of (BW11Co/Ha)n films is superior to that of POM-free hemicyanine dye films. POM components can significantly improve the photocurrent generation properties of hemicyanine dyes by efficient electron transference between the ITO electrode and the hemicyanine, and retardation of recombination reaction in photoelectrochemical cells. This study would guide molecular design for more efficient photoelectrocatalytic, and energy conversion and storage devices.

From Geometry to Activity: A Quantitative Analysis of WO3/Si Micropillar Arrays for Photoelectrochemical Water Splitting

AbstractThe photoelectrochemical (PEC) activity of microstructured electrodes remains low despite the highly enlarged surface area and enhanced light harvesting. To obtain a deeper understanding of the effect of 3D geometry on the PEC performance, well‐defined WO3/n‐Si and WO3/pn‐Si micropillar arrays are fabricated and subjected to a quantitative analysis of the relationship between the geometry of the micropillars (length, pitch) and their PEC activity. For WO3/n‐Si micropillars, it is found that the photocurrent increases for WO3/n‐Si pillars, but not in proportion to the increase in surface area that results from increased pillar length or reduced pillar pitch. Optical simulations show that a reduced pillar pitch results in areas of low light intensity due to a shadowing effect. For WO3/pn‐Si micropillar photoelectrodes, the p–n junction enhances the photocurrent density up to a factor of 4 at low applied bias potential (0.8 V vs RHE) compared to the WO3/n‐Si. However, the enhancement in photocurrent density increases first and then decreases with reduced pillar pitch, which scales with the photovoltage generated by the p–n junction. This is related to an increased dead layer of the p–n junction Si surface, which results in a decreased photovoltage even though the total surface area increases.

Visible-light photoelectrochemical sensor for glutathione based on CoFe2O4-nanosphere-sensitized copper tetraaminophthalocyanine–graphene oxide

Simple, fast, and sensitive detection methods are required for reduced glutathione (GSH), a metabolic substance that acts as an indicator for a variety of diseases and is also found in numerous supplements and drugs. Herein, a sensitive and selective photoelectrochemical (PEC) sensor was developed for GSH detection. The novel PEC sensor was fabricated using CoFe2O4 nanoporous spheres and copper tetraaminophthalocyanine–graphene oxide (CuTAPc-GO) as photoelectric materials. Under illumination, CoFe2O4 facilitated the spatial separation of the photogenerated charge carriers in CuTAPc-GO, thereby enhancing the photocurrent signal of the PEC sensor. The influences of pH, CoFe2O4 amount, coating amount, and applied bias potential on the PEC response toward GSH were investigated. Under optimized conditions, the designed PEC sensor presented a wide linear response range for GSH of 0.25–320 μM with a detection limit of 0.016 μM at a signal-to-noise ratio of 3. Moreover, this PEC sensor exhibited excellent selectivity, reproducibility, and stability, showing satisfactory results for the detection of GSH in urine and pharmaceutical drugs.

Grand canonical simulations of ions between charged conducting surfaces using exact 3D Ewald summations.

We present a useful methodology to simulate ionic fluids confined by two charged and perfectly conducting surfaces. Electrostatic interactions are treated using a modified 3D Ewald sum, which accounts for all image charges across the conductors, as well as the 2D periodicity, parallel to the surfaces. The energy expression is exact, and the method is trivial to implement in existing Ewald codes. We furthermore invoke a grand canonical scheme that utilizes a bias potential, that regulates the surface charge density. The applied bias potential also enables us to calculate individual chemical potentials of the ions. Finally, we argue that our approach leads to a pedagogically appealing description of the Donnan potential, and what it measures in these systems.

Photoelectrocatalytic degradation of Ag-cyanide complexes and synchronous recovery of metallic Ag driven by TiO2 nanorods array photoanode combined with titanium cathode.

A photoelectrocatalytic (PEC) system for the decomposition of Ag-cyanide complexes synchronously with Ag recovery was established using the titanium dioxide nanorods (TiO2 NRs) as photoanode and the titanium plate as cathode. The removal efficiency of total cyanide was 76.58%, and the recovery ratio of Ag achieved 84.48% at the applied bias potential of 1.0 V vs SCE in the PEC process. During the reaction, the surface variations and photo-electric properties of TiO2 NRs photoanode or titanium cathode were characterized by SEM-EDS, XPS, and photoelectronic analyses. It was indicated that Ag2O and metallic Ag were deposited onto the TiO2 NRs photoanode and titanium cathode, respectively. Specifically, the in situ generated Ag2O on the TiO2 NRs photoanode facilitated the separation of the photogenerated charge carriers and enhanced the visible-light response, thus improving its PEC catalytic activity toward cyanide destruction. Combined with the results of active species quenching experiments, the mechanism of Ag-cyanide complexes decomposition and metallic Ag recovery by the PEC process was proposed.

Thermodynamic and Kinetic Control of Photoelectrochemical CO2 Reduction into Liquid Fuels

In the photoelectrochemical CO2 reduction reaction, water oxidation reaction is performed on 040-BVO and chemical fuels is obtained on Cu cathode in the CO2-saturated NaCl electrolyte under AM 1.5 G. C1 chemical fuel is evolved through reduction potential depending multistep process from CO2 molecule. 040-BVO(photoanode)/NaCl(electrolyte)/Cu(cathode) system is illuminated with solar light under the external bias that is tailored to reduce CO2 via reduction potential tuning. Integrating applied bias potential into conduction band minimum of 040-BVO enables CO2 molecules to be converted into valuable chemical fuels. We observe that the selectivity and yield of the products depend on CO2 reduction potential tuning. With water oxidation reaction of 040-BVO photoanode which has 42.1% of the absorbed photon-to-current conversion efficiency at 1.23 V (vs RHE), chemical products were observed as faradaic efficiency of 30% formic acid, 60% formaldehyde, 12% MeOH and 3% EtOH by reduction potential tuning. For this study, the correlation between the production of solar chemical fuels and CO2 reduction potential tuning via external bias potential on 040-BVO photoanode/Cu photocathode is systematically investigated. Keywords: Artificial photosynthesis; Multi-electron shuttling; CO2 reduction potential tuning

Taguchi method for optimization of immobilized Dy2O3/graphite/TiO2/Ti nanocomposite preparation and application in visible light photoelectrocatalysis process

In the first section of work, Taguchi's L9 orthogonal design was applied to investigate the effect of Dy2O3 and graphite masses, calcination temperature and voltage to prepare a new and optimized Dy2O3/graphite/TiO2/Ti electrode through the electrophoretic deposition process. The obtained optimum conditions with considering the visible light photoelectrocatalytic ability in decolorization and electrode stability were as follows: 7 mg Dy2O3, 50 mg graphite, calcination temperature of 400 °C and different voltage of 60 V. The results of SEM, EDX elemental mapping and XRD for the optimized Dy2O3/graphite/TiO2/Ti electrode indicated the uniform immobilization of Dy2O3, graphite and TiO2 particles on the Ti grid sheet. Moreover, the DRS approved the photo-absorption ability of the prepared electrode in the visible light range.In the second part, Taguchi's L16 orthogonal design was used to investigate the effect of pH, the number of Dy2O3/graphite/TiO2/Ti electrode(s), visible light power and applied bias potential on the photoelectrocatalytic ability of the prepared electrodes in the degradation of Maxilon Blue from well water. The obtained results showed that the maximum decolorization efficiency was achieved at the optimum conditions: pH of 10, two Dy2O3/graphite/TiO2/Ti electrodes, visible light power of 72 W and applied bias potential of 0.9 V. The decolorization efficiency of the photoelectrocatalysis process using the optimized electrodes was considerably higher than solo sorption, electrosorption and photolysis processes.

Mapping the perturbation potential of metallic and dipolar tips in tunneling spectroscopy on MoS2

Scanning tunneling spectroscopy requires the application of a potential difference between the sample and a tip. In metal-vacuum-metal junctions, one can safely assume that the potential is constant along the metallic substrate. Here, we show that the inhomogeneous shape of the electric potential has to be taken into account when probing spatially extended molecules on a decoupling layer. To this end, oligothiophene-based molecules were deposited on a monolayer of molybdenum disulfide (MoS$_2$) on a Au(111) surface. By probing the delocalized molecular orbital along the thiophene-backbone, we found an apparent intramolecular shift of the positive ion resonance, which can be ascribed to a perturbation potential caused by the tip. Using a simple model for the electrostatic landscape, we show that such a perturbation is caused by the inhomogeneity of the applied bias potential in the junction and may be further modified by an electric dipole of a functionalized tip. The two effects can be disentangled in tunneling spectra by probing the apparent energy shift of vibronic resonances along the molecular backbone. We suggest that extended molecules on MoS$_2$ can be used as a sensor for the shape of the electrostatic potential of arbitrary tips.

Photoswitching and photocatalytic functions of SnxCu1−xS nanostructures

Ultra-thin semiconducting nanostructures are garnering strategic importance in energy and environment remediation applications. In this regard, SnxCu1−xS nanostructures were processed through an eco-friendly chemical route and investigated in detail for photoswitching and photocatalytic functions. X-ray diffraction, FT-IR, Raman, UV–vis absorbance and high-resolution microscopic tools were initially used to examine the physico-chemical traits of SnxCu1−xS nanostructures. Ambiguous evidence for the substitution of Sn ions in place of Cu ions was attained through X-ray photoelectron spectroscopy. The photocatalytic performance of SnxCu1−xS systems was investigated through effective remediation of organic dye molecules under visible light. Scavenger based photocatalytic experiments were additionally carried out to infer the degradation mechanism. Type II p-n SnxCu1−xS/In2S3 heterojunction diodes were also demonstrated for the first time with improved electrical conductivity and photoelectrical performances. The rectification ratio, forward current values and photo switching capabilities of these diodes were noted to improve in the Current vs. Voltage (I-V) and Current vs. Time (I-T) curves as a function of Sn composition and applied bias potential. The excellent photo switching stability augments the photo generated carriers to be effectively separated along the p-n junctions. The enhanced photoelectronic and photocatalytic functionalities in SnxCu1−xS has finally been reasoned to the improved charge transfer kinetics in the respective architectures, resulting from the effective Sn interaction in hexagonal host lattice.

Electrical and electrochemical behavior of a zinc-rich epoxy coating system with carbon nanotubes as a diode-like material

Non-conventional responses in the impedance spectra of a zinc-rich coating system were observed in electrical and electrochemical impedance measurements that have previously been considered to have no effect on the system. Despite the impressive progress in zinc-rich coating systems to control corrosion in metal structures through galvanic effects, some physical properties influencing the responses of electrochemical systems remain unexplored. Electrochemical and non-electrolytic cells on zinc-rich (55 vol%) coatings with multi-wall carbon nanotube systems were analyzed to determine the intrinsic response of the coating with electrical passive and active analogs under electrical conditioning cycles. In the dry condition, the impedance spectra of the carbon nanotube-added zinc-rich coating showed increased electrical resistance of the film under consecutive cyclic testing. The non-conventional response of the increase in impedance was studied by determining the impedance responses under various temperatures and bias potentials and performing a current-voltage method. The non-conventional phenomenon was found to be caused by an increased barrier height between the semiconducting zinc oxide material and metal, which is susceptible to an external electrical field. During immersion, the change in impedance of the zinc-rich primer (ZRP) film under consecutive electrochemical sequences differed from that under natural degradation. This non-conventional response of the ZRP coating was influenced by the applied bias potential. The capacitive behavior influenced by the zinc corrosion products in the coating had a longer relaxation time, thus decreasing the open circuit potential. To understand this phenomenon, we propose a charging-relaxation potential model. In addition, the potential exhibited a change in the electrical resistance of the ZRP film during consecutive electrochemical testing.

Metal chalcogenide based photocatalysts decorated with heteroatom doped reduced graphene oxide for photocatalytic and photoelectrochemical hydrogen production

Heteroatom (N, B and P) doped reduced graphene oxide (RGO)-metal chalcogenide nanocomposites (RGO-Cd0.60Zn0.40S) were prepared by the solvothermal method, and then they were characterized with X-ray diffraction, Raman spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, UV–Vis diffuse reflectance spectroscopy and photoluminescence techniques. Doping of RGO with heteroatoms of N, B and P increased charge-transfer capability of nanocomposites and thus, improved both photocatalytic and photoelectrochemical hydrogen production activities of them. N-doped RGO-Cd0.60Zn0.40S photocatalyst exhibited the highest photocatalytic hydrogen production rate (1114 μmolh−1 g−1) in photocatalytic (PC) system amongst other and it was 1.5 times higher than that of RGO-Cd0.60Zn0.40S photocatalyst. Having a current density of 0.92 mAcm−2, photoelectrochemical hydrogen production activity of N-RGO-Cd0.60Zn0.40S electrode was found to be 3 times higher than RGO-Cd0.60Zn0.40S photoelectrode without any applied bias potential under visible light irradiation in photoelectrochemical system. In general, these results clearly showed that heteroatom doping of RGO led to promising materials for renewable hydrogen production in the photocatalytic and photoelectrochemical systems.

Visible light photoelectrocatalysis for wastewater treatment using bifacial N-TiO2/Graphene/Ho2O3/Titanium nanocomposite: Artificial neural network modeling and evaluation of ozone addition

In this paper, N-TiO2/Graphene/Ho2O3/Titanium bifacial nanocomposite electrode was prepared. First, the effect of Ho2O3 to N-TiO2 wt.% in the nanocomposite preparation matrix was investigated through studying visible light photoelectrocatalysis process in industrial wastewater decolorization. Characterizations of optimum catalyst were performed using DRS, XRD, SEM and EDX analyses. Then, the effect of operating variables i.e. catalyst dosage (electrode number(s)), wastewater pH, applied bias potential, visible light power and contact time on the extent of wastewater decolorization was investigated by the visible light photoelectrocatalysis process. It was observed that almost 80% wastewater decolorization was achieved using the photoelectrocatalysis at the optimum conditions by N-TiO2/Graphene/(10%) Ho2O3. Artificial neural network was used for model the photoelectrocatalysis process and determine the relative importance of investigated operating variables. It was also established that combination of photoelectrocatalysis with ozonation yielded 100% decolorization in 90 min and 96% COD removal in 270 min under the optimized conditions. Moreover, the catalyst sheet was enough stable to be used in all wastewater treatment experiments.

Preparation of rGO/AgCl QDs and its enhanced photoelectrocatalytic performance for the degradation of Tetracycline

AbstractA novel rGO/AgCl QDs composites have been obtained by an ultrasonic‐assisted method for the first time. Photoelectrocatalytic (PEC) performances of the obtained samples were studied by the degradation of 20 mg/L Tetracycline (TC) under visible light irradiation with an applied bias potential of 1.5 V (vs Ag/AgCl). Degradation of TC by different processes including Photocatalysis (PC), Electrocatalysis (EC), and PEC was compared, and the effect of different bias potential on the PEC degradation of TC was discussed. Results showed that rGO/AgCl QDs composites had displayed superior PEC activity than that of pristine AgCl QDs with degrading 85.2% of TC during 120 minutes, which was about 1.5 times higher than that of AgCl QDs (33%). Besides, compared to PC and EC removal of TC, PEC process showed the highest degradation efficiency of TC (85.2%) by rGO/AgCl QDs, which was about three times and one time higher than that of PC (39.18%) and EC (20.73%) system, respectively. Moreover, the reusibility and stability of the samples were tested by five times cycling tests, and results demonstrated that the stability of bare AgCl QDs was improved after the introduction of rGO. The enhanced PEC activity and stability of the samples could be attributed to the intimate contact between rGO and AgCl QDs and external electric field, which had benefitted the formation of more active sites and accelerated electron‐hole separation.