Adsorbed Hydroxyl Groups Research Articles

Synergistic degradation of methylene blue by laser cavitation and activated carbon fiber

Methylene blue is widely used, but highly toxic and difficult to be degraded. In this paper, a new method of synergistic degradation of methylene blue by laser cavitation and activated carbon fiber is proposed. This paper theoretically studies the synergistic degradation effect, including radical oxidation effect, shock wave breakdown effect and activated carbon fiber surface adsorption effect. The deep degradation of methylene blue was studied experimentally, and the key influencing factors were analyzed. The results show that: the reason why methylene blue can be degraded is because of the oxidation effect of hydroxyl radicals, thermal decomposition and adsorption of molecules on the surface of carbon fibers. The main factors affecting the degradation rate of methylene blue solution are laser energy and initial concentration of solution. The degradation rate increased by 37.4% with the increase of laser energy (12–48 mJ) and decreased by 2.6% with the increase of initial concentration (0.01–0.05 mg/ml). The maximum degradation rate (93%) of methylene blue solution was reached at 48 mJ and 0.01 mg/ml for 30 min. Compared with the traditional adsorption degradation of carbon fibers, the degradation rate of the synergistic degradation of methylene blue solution by laser cavitation and activated carbon fibers can be increased by about 80% in a short time (30 min).

NiFe Alloy Electrocatalysts toward Efficient Alkaline Hydrogen Oxidation

AbstractWe report the pyrolysis of NiFe‐containing nanocrystals, which leads to 10.2±2.4 nm NiFe alloy particles embedded in carbon with an exceptional area specific exchange current density of 0.048 mA cmNi−2 toward the alkaline hydrogen oxidation reaction (HOR). The high activity primarily originates from optimized hydrogen and hydroxyl adsorption strength due to alloying effect between Ni and Fe.

In Situ Surface PtCu Alloying on Delafossite-type CuAlO2 as Electrocatalyst for Enhanced Methanol Oxidation

Delafossite type oxide CuAlO2 as a highly efficient methanol oxidation reaction catalyst support has been investigated in this work. Utilizing the sustained release of copper from CuAlO2 layered structure, we developed a composite catalyst that was in situ formed PtCu alloy upon oxide via solvothermal method. Owing to the metal-support interaction between PtCu alloy and CuAlO2, abundant oxygen defects and adsorbed hydroxyl groups were generated on the surface of composite catalyst, which were verified by structural characterizations and surface analysis. Density functional theory simulation further revealed that the in situ formation of PtCu alloy accompanied with superficial defects dramatically changed the geometry and electronic structures of the composite catalyst, resulting in a higher mass activity (990 mA/mgPt), specific activity (3.30 mA cm−2 ECSA), and a superior reaction kinetics of MOR performance. This work proves delafossite type oxide CuAlO2 as a potential support to facilitate the anti-CO poisoning ability of Pt-based catalysts.

Multi-hierarchical cobalt-based electrocatalyst towards high rate H2 production

Herein, a rational design of “cobalt/cobalt oxide/cobalt molybdate/nickel foam” multi-hierarchical tandem type electrocatalyst was achieved, where in situ reduced Co and CoO nanoparticles were dispersed uniformly and stabilized by CoMoO3 cuboids. This novel tandem type structure enables strong hydroxyl adsorption on CoO and moderated hydrogen adsorption on Co and therefore promotes the dissociation of water and the recombination of hydrogen intermediates into molecular hydrogen, respectively, and both act synergistically to catalyze the HER reaction. As a result, the current densities were up to 1.3 A cm−2 at only 173 mV overpotential in 1.0 M KOH and 379 mV in 1.0 M PBS solution, respectively. The high rate H2 production of 4.35 ml min−1 at − 1.18 V (vs. SCE) and the outstanding performance of 10 A lasting for more than 800 h in a MEA electrolyzer both indicate the prospect for the usage in practical.

Tuning the hydrogen and hydroxyl adsorption on Ru nanoparticles for hydrogen electrode reactions via size controlling

Controlling the particle size of catalyst to understand the active sites is the key to design efficient electrocatalysts toward hydrogen electrode reactions including hydrogen oxidation and evolution (HOR/HER). Herein, the hydrogen and hydroxyl adsorption on Ru/C could be effectively tuned for HOR/HER by simple controlling the particle sizes. It is found that the metallic Ru (Ru0) is the active site for HOR/HER, while oxidized Ru (Rux+) will hinder the adsorption and desorption of hydrogen on the catalyst. For the HOR, catalyst with small particles is more efficient, due to it is a three-phase interface reaction of gas on the surface of the catalyst. For the HER, the metallic state of Ru is crucial. The deconvolution of hydrogen peaks indicates that the catalytic sites with low hydrogen binding energy (HBE) shoulder the majority of the HOR activity. CO stripping curve further demonstrates that the stronger hydroxyl species (OHad) affinity is beneficial to promote the HOR performance. The results indicate that the design of efficient HOR/HER catalyst should focus on the balance between particle size and metallic states.

Platinum-Ruthenium Single Atom Alloy as a Bifunctional Electrocatalyst toward Methanol and Hydrogen Oxidation Reactions.

The precise regulation for the structural properties of nanomaterials at the atomic scale is an effective strategy to develop high-performance catalysts. Herein, a facile dual-regulation approach was developed to successfully synthesize Ru1Ptn single atom alloy (SAA) with atomic Ru dispersed in Pt nanocrystals. High-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure demonstrated that Ru atoms were dispersed in Pt nanocrystals as single atoms. Impressively, the Ru1Ptn-SAA exhibited an ultrahigh specific activity (23.59 mA cm-2) and mass activity (2.805 mA/μg-PtRu) for methanol oxidation reaction (MOR) and exhibited excellent exchange current density activity (1.992 mA cm-2) and mass activity (4.71 mA/μg-PtRu) for hydrogen oxidation reaction (HOR). Density functional theory calculations revealed that the introduction of Ru atoms greatly reduced the reaction free energy for the decomposition of water molecules, which promoted the removal of CO* in the MOR process and adjusted the Gibbs free energy of hydrogen and hydroxyl adsorption to promote the HOR. Our work provided an effective idea for the development of high performance electrocatalysts.

Operando deciphering the activity origins for potential-induced reconstructed oxygen-evolving catalysts

Fe incorporated Ni-based electrocatalysts have emerged as one of the most active oxygen-evolving catalysts under alkaline conditions and deciphering the effect of iron incorporation in enhancing the activity is challenging but critical for the catalyst design. Herein, the as-prepared nanocube Ni-based catalysts underwent a reconstruction process and transformed from γ-NiOOH to β-NiOOH structure by iron incorporation under the applied bias, which was confirmed by in-situ Raman measurement. According to the methanol oxidation current response difference, the hydroxyl adsorption intensity was proposed to be regulated by iron incorporation and the rate-determining step would be the formation of *OOH for Fe-doped β-NiOOH, which was further supported by DFT calculation. This work reveals the effect of iron-doped on the phase structure transform and the regulation of intermediate species elaborately and offers new insight on the understanding of the activity origins for NiFe-based catalysts.

Engineering asymmetric Fe coordination centers with hydroxyl adsorption for efficient and durable oxygen reduction catalysis

Single-atom Fe catalysts are a promising substitute to Pt catalysts for oxygen reduction reaction (ORR). Adjusting metal energy level through direct atomic interface regulation can effectively improve catalytic performance but still in its infancy. Herein, highly active nitrogen and sulfur dual-coordinated asymmetric Fe center anchored in carbon nanoparticles were developed. Spontaneously absorbed OH ligand is steadily anchored in asymmetric atomic interface, constructing new FeN3S-OH moiety. Theoretical calculations reveal that the incorporated S atom combined with OH ligand as energy level modifier effectively activate Fe center by electronic modulation and d-band center shift, rendering improved ORR activity of FeNSC-2Fe with E1/2 of 0.913 V in alkaline, 0.806 V in acidic and 0.711 V in neutral media. The FeNSC-2Fe-based device displays high power density of 306 mW cm−2 in Zn-air battery and 2485 mW m−2 in microbial fuel cell. This work provides a new perspective for the controllable synthesis and performance optimization for electrocatalysts.

The morphology, crystal structure and oxygen evolution reaction electrocatalysis performance of scandium-doped MIL-101(Fe)

The oxygen evolution reaction (OER) electrocatalyst is highly desirable as it plays an important role in many energy conversion technologies by effectively reducing the OER process overpotential. Herein, the morphology, crystal structure and more importantly, the OER electrochemical activity of Scandium-doped MIL-101(Fe) were investigated. It was found that the competitive nucleation as well as the difference in the oxytropism between Sc3+ and Fe3+ ions, which lead to the crystalline structure change and consequently the morphology evolved from quadrangular star-shaped bipyramid to hexagonal bipyramids. Moreover, the OER electrocatalysis performance was improved significantly when incorporation Sc3+ ion into the MIL-101(Fe) host body. The X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the strong bimetal interaction between Fe3+ and Sc3+ ions, leading to well-modified Fe3+ electronic structure. It yielded optimal hydroxyl adsorption energy on Fe3+ and thus facilitated the process of O2 evolution. Such Sc3+ ion doping strategy to modulate the OER performance was also extendable to other Metal-organic frameworks (MOFs) structures. It demonstrates a better OER activity with a low overpotential of 300 ​mV at 10.0 ​mA ​cm−2 and Tafel slope of 125 ​mV dec−1 for Sc-CoBDC-3, which provides great potential for fabricating optimal OER MOFs.

Surface-Terminated Hydroxyl Groups for Deciphering the Facet-Dependent Photocatalysis of Anatase TiO2.

Understanding the relation between a crystal facet and photocatalytic performance is of great importance for the development of effective catalysts. In this work, we focus on anatase TiO2 with controllable exposed facets toward photocatalytic hydrogen evolution by water splitting. By combining temperature-programmed desorption (TPD) and diffuse reflectance infrared spectroscopy (DRIFTS), we obtain that the adsorption of hydroxyl groups and the photo-driven breaking of hydroxyl groups depend strongly on the exposed facets. As a result, the higher catalytic hydrogen evolution activity of TiO2 enclosed with (101) facets than that of (001) facets should be ascribed to the more favorable depletion of hydroxyl groups. Moreover, graphene quantum dots (GQDs) with rich surface functional groups are deliberately deposited on the TiO2 surface. The determination of the states and dynamics of surface hydroxyl groups suggests that GQDs facilitate the reaction of hydroxyl groups on (001)TiO2, thus leading to the activity enhancement. By contrast, the already active (101)TiO2 become apparently less efficient after GQD deposition due to the restricted reaction of hydroxyl groups. Overall, our findings not only provide a unique guidance for understanding the crystal-plane-dependent photocatalysis but also present a powerful approach by which to tailor the photocatalytic performance.

Selective Photoelectrocatalytic Glycerol Oxidation to Dihydroxyacetone via Enhanced Middle Hydroxyl Adsorption over a Bi2O3-Incorporated Catalyst.

Photoelectrocatalytic (PEC) glycerol oxidation offers a sustainable approach to produce dihydroxyacetone (DHA) as a valuable chemical, which can find use in cosmetic, pharmaceutical industries, etc. However, it still suffers from the low selectivity (≤60%) that substantially limits the application. Here, we report the PEC oxidation of glycerol to DHA with a selectivity of 75.4% over a heterogeneous photoanode of Bi2O3 nanoparticles on TiO2 nanorod arrays (Bi2O3/TiO2). The selectivity of DHA can be maintained at ∼65% under a relatively high conversion of glycerol (∼50%). The existing p-n junction between Bi2O3 and TiO2 promotes charge transfer and thus guarantees high photocurrent density. Experimental combined with theoretical studies reveal that Bi2O3 prefers to interact with the middle hydroxyl of glycerol that facilitates the selective oxidation of glycerol to DHA. Comprehensive reaction mechanism studies suggest that the reaction follows two parallel pathways, including electrophilic OH* (major) and lattice oxygen (minor) oxidations. Finally, we designed a self-powered PEC system, achieving a DHA productivity of 1.04 mg cm-2 h-1 with >70% selectivity and a H2 productivity of 0.32 mL cm-2 h-1. This work may shed light on the potential of PEC strategy for biomass valorization toward value-added products via PEC anode surface engineering.

Photocatalytic Selective Degradation of Catechol and Resorcinol on the TiO2 with Exposed {001} Facets: Roles of Two Types of Hydroxyl Radicals

Photocatalytic studies on contaminant degradation in water suspension generally suggest that the degradation reaction mainly takes place on the surface of the photocatalysts rather than in the water phase. The mechanism of selective degradation is often difficult to distinguish concerning the contribution of adsorption and radical selectivity. This study is thus designed to investigate the roles of two types of hydroxyl radicals, adsorbed hydroxyl radical (·OHa) and free hydroxyl radical (·OHf), on the selective degradation of catechol (CT) and resorcinol (RE). CT and RE are significantly different in adsorption on a TiO2 photocatalyst with a highly exposed {001} facet. CT can be selectively degraded by TiO2 and was highly correlated with adsorption. Free radical quenching experiment results showed that the degradation of CT can be identified as the combined effect of both ·OHa and ·OHf, while the degradation of RE was mainly due to the ·OHf. Electron paramagnetic resonance coupled with spin trapping agents was used to detect the relative concentration of hydroxyl radicals in all the photocatalytic degradation processes. After a series analysis, we proposed that the mechanism of selective degradation mainly depends on the concentration of ·OHf for the pollutant molecules with weak adsorption on the catalyst surface.

Interface engineering of in−situ formed nickel hydr(oxy)oxides on nickel nitrides to boost alkaline hydrogen electrocatalysis

Highly efficient platinum−group−metal (PGM) free catalysts for alkaline hydrogen oxidation reaction (HOR) are of vital issues for the development of alkaline hydroxide exchange membrane fuel cells (HEMFCs). Herein, with the help of interface engineering by the in−situ electrochemical surface reconfiguration strategy, the seamless nickel nitrides-nickel hydr(oxy)oxide (denoted as Ni3N−Ni(OH)2) heterostructures were developed. From the systematic electrochemical measurements, the impressive HOR performance such as nearly zero onset overpotential, larger exchange current density, excellent long−term durability, and robust CO tolerance in alkaline media, are obtained by the optimized Ni3N−Ni(OH)2 catalyst, thus rendering it significant potential for applications in HEMFCs. Furthermore, this catalyst also exhibits superior HER activity, approaching to that of Pt/C catalyst. The tailored d band center of Ni and the enhanced hydroxyl adsorption ability at Ni3N−Ni(OH)2 heterojunctions are evidenced by the comprehensive spectroscopy and electrochemical analyses, which are favorable for the accelerated Volmer step toward alkaline hydrogen electrocatalysis.

Understanding the selectivity trend of water and sulfate (SO42−) oxidation on metal oxides: On-site synthesis of persulfate, H2O2 for wastewater treatment

Herein, H2O2 production activity via two-electron water oxidation reaction is identified on metal oxides (WO3, TiO2, and BiVO4) in acidic SO42− involving electrolyte, in which persulfate (PS) acts as an intermediate. A deep understanding of mechanism of PS production reaction on metal oxides has been realized based on rigorous crystal plane analysis of WO3 and TiO2 by combining density functional theory calculations and zeta potential measurements. It is found that the binding-energy of adsorbed hydroxyl groups on dominant exposed crystal plane of WO3 is lower than that of TiO2, leading to more SO42− adsorption sites at the surface of WO3. Consequently, the formation of PS on WO3 surface is more favorable. Meanwhile, both SO4−· and OH· were detected in the electrolyte by electron paramagnetic resonance measurement, which play a crucial role in organic pollutants wastewater treatment, with a degradation efficiency of 96% in 90 min for a typical pollutant norfloxacin. This work can provide a novel insight for understanding the selectivity of water and SO42− species oxidation on metal oxides, and open a new way for both on-site H2O2 production and advanced oxidation processes application.

A universal chemical-induced tensile strain tuning strategy to boost oxygen-evolving electrocatalysis on perovskite oxides

Exploring effective, facile, and universal tuning strategies to optimize material physicochemical properties and catalysis processes is critical for many sustainable energy systems, but still challenging. Herein, we succeed to introduce tensile strain into various perovskites via a facile thermochemical reduction method, which can greatly improve material performance for the bottleneck oxygen-evolving reaction in water electrolysis. As an ideal proof-of-concept, such a chemical-induced tensile strain turns hydrophobic Ba5Co4.17Fe0.83O14-δ perovskite into the hydrophilic one by modulating its solid–liquid tension, contributing to its beneficial adsorption of important hydroxyl reactants as evidenced by fast operando spectroscopy. Both surface-sensitive and bulk-sensitive absorption spectra show that this strategy introduces oxygen vacancies into the saturated face-sharing Co-O motifs of Ba5Co4.17Fe0.83O14-δ and transforms such local structures into the unsaturated edge-sharing units with positive charges and enlarged electrochemical active areas, creating a molecular-level hydroxyl pool. Theoretical computations reveal that this strategy well reduces the thermodynamic energy barrier for hydroxyl adsorption, lowers the electronic work function, and optimizes the charge/electrostatic potential distribution to facilitate the electron transport between active sites and hydroxyl reactants. Also, this strategy is reliable for other single, double, and Ruddlesden–Popper perovskites. We believe that this finding will enlighten rational material design and in-depth understanding for many potential applications.

Hydroxyl Adsorption Derived Reactive Oxygen Species from Carbon Paper-Supported Cu2o for Enhanced Electrochemical Glucose Sensing

Hydroxyl Adsorption Derived Reactive Oxygen Species from Carbon Paper-Supported Cu2o for Enhanced Electrochemical Glucose Sensing

A synergistic architecture design for functionally boosting the hydroxyl adsorption and charge transfer for the oxygen evolution reaction

A material with a karren-structure and hybrid phase is preparedviaa molten-salt treatment. This novel architecture regulates the morphology and electronic properties, synergistically expediting the sluggish OER kinetics.

Fluorescence Enhancement of Lignin-Based Carbon Quantum Dots by Concentration-Dependent and Electron-Donating Substituent Synergy and Their Cell Imaging Applications.

Black liquor is an important pollutant in the pulp industry, but it also has the potential for high-value utilization. In this study, lignin extracted from black liquor was hydrothermally prepared into lignin-based carbon quantum dots (L-CQDs) using a one-pot method. Physicochemical characterization suggested that the L-CQDs exhibited a lamellar core-shell multilayered graphene structure surrounded by oxygen-containing functional groups. The fluorescence intensity of the L-CQDs was strengthened depending on their own concentration dependence and the doping of external groups. The fluorescence intensity of L-CQDs varied between 89.09 and 183.66 under different concentrations, and the most intense fluorescence (183.66) was obtained at 0.1 mg mL-1. At hydroxyl and amino adsorption capacities of 11.08 and 0.98 mmol g-1, the hydroxylated RL-CQDs-5 and aminated NL-CQDs-3 exhibited the highest fluorescence intensities at 689.22 and 605.39, respectively. Moreover, when pristine L-CQDs were sequentially aminated and hydroxylated, the NRL-CQDs' fluorescence intensity reached 1224.92. Cell imaging experiments proved that cells cultivated with NRL-CQDs have brighter fluorescence compared with L-CQDs. The results will render L-CQDs more suitable for practical applications.

Tuning oxygen vacancies on LaFeO3 perovskite as efficient electrocatalysts for oxygen evolution reaction

The oxygen vacancies in lanthanum-iron oxide perovskite were produced by plasma. The vacancy concentration was facilely tuned by plasma forming-gas following the order of Ar > O2 > H2/Ar. The oxygen vacancies obviously promoted oxygen evolution reaction (OER) performance. O2-plasma produced a moderate concentration of oxygen vacancy in LaFeO3 which exhibited the highest OER activity. DFT calculations confirmed that the weak hydroxyl adsorption was improved by oxygen vacancy, but excessive oxygen vacancies reduced the OER activity with strong hydroxyl adsorption energy.

Radiation damage and abnormal photoluminescence enhancement of multilayer MoS2 under neutron irradiation

In this work, neutron irradiation effects on the optical property of multilayer MoS2 have been investigated in depth. Our results display that the intensity of the photoluminescence (PL) spectra of MoS2 flakes tends to slightly decrease after exposed to neutron irradiation with low fluence of 4.0 × 108 n/cm2. An unexpected improvement of PL intensity, however, is observed when the irradiation fluence accumulates to 3.2 × 109 n/cm2. Combined with the experimental results and first-principles calculations, neutron irradiation damage effects of multilayer MoS2 are analyzed deeply. Sulfur vacancy (V S) is found to be responsible for the attenuation of the PL intensity as a major defect. In addition, our results reveal that the adsorbed hydroxyl groups (OH) and oxygen atoms (O) on the surface of MoS2 flakes not only promote the transition from trion excitons to neutral excitons, but also repair the V S in MoS2, both of which contribute to the enhancement of luminescence properties. The detailed evolution process of irradiation-induced defects is discussed to reveal the microscopic mechanism of the significantly difference in luminescence intensity of MoS2 under different irradiation stages. This work has great significance for evaluating the neutron radiation hardness of multilayer MoS2, which is helpful to enrich the fundamental research on neutron irradiation effects.