As-synthesized Catalysts Research Articles

Fabrication of Flower-like Rhodium-Doped β-Ni(OH)2 as an Efficient Electrocatalyst for Methanol Oxidation Reaction in Alkaline Media

In this study, β-Ni(OH)2 with a unique flower-like morphology was synthesized through a hydrothermal method. The doping of Rh in β-Ni(OH)2 was achieved by a reduction method. The as-synthesized catalysts were characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy for the crystal structure, morphology, composition, and chemical state analysis. The electrochemical tests revealed that the doping of Rh can significantly increase the electrocatalytic performance of β-Ni(OH)2 in 1.0 M KOH solution. The methanol oxidation peak current density of Rh-doped β-Ni(OH)2 reached 95 mA cm-2 with a Tafel slope of 40 mV dec-1. The reason for these improvements is that Rh can suppress the phase transformation of NiOOH from β to α. Meanwhile, the electronic structure change of nickel in β-Ni(OH)2 and the defect ratio increase caused by Rh doping are beneficial to methanol oxidation reaction (MOR) catalytic activity. Furthermore, the synergistic effect between Rh and Ni(OH)2 improved the surface activity of β-NiOOH. The doping of Rh in β-Ni(OH)2 is initiative in this work, which provides a new strategy to design highly efficient and cost-effective MOR electrocatalysts for alkaline DMFCs.

Gold nanoparticles self-assemble on the thiol-functionalized fibrous silica microspheres to produce a robust catalyst

A new type of catalyst based on thiol-functionalized fibrous nano-silica material (DFNS-SH) with unique fibrous structure as support and gold nanoparticles (Au NPs) as active sites (DFNS-SH/Au) has been prepared through a facile and environment-friendly self-assembly approach. The synthetic procedure involves the Au NPs prepared in mild conditions instantaneously self-assembled onto the DFNS-SH. The as-synthesized catalyst exhibits a remarkable higher catalytic activity in the reduction of 4-nitrophenol compared with other recently reported related catalysts. Furthermore, DFNS-SH/Au has an outstanding recyclability, after repeated use for many times, obvious activity loss did not occur until the eleventh time. The excellent catalytic activity and robust recyclability are attributed to the synergistic effect between the DFNS-SH and Au NPs. Numerous nano-fibers appear on DFNS-SH, which effectively enhance the mass diffusion and transport in catalytic reactions. Additionally, the enough strong interaction between the Au NPs and thiol groups onto the surface of DFNS can efficiently protect the Au NPs from aggregation and also endow the DFNS-SH/Au with enhanced stability. Thiol groups are also beneficial for improving the Au loading, decreasing the NPs size, reducing their aggregation and improving the catalytic performance of Au NPs anchored on the DFNS-SH as much as possible. This synthetic method discovers an eco-friendly path to effectively prepare low-budget Au-based catalysts and is promising for the development of other excellent materials.

Development of Bi2WO6 and Bi2O3 - ZnO heterostructure for enhanced photocatalytic mineralization of Bisphenol A.

Present study proposed the synthesis of mixed p-type and n-type nanocomposite heterostructures by co-precipitation method. The as-synthesized heterostructures were characterized through different characterization techniques. The as-synthesized Bi2WO6 and Bi2O3-ZnO heterostructures were tested as photocatalysts during the photodegradation of Bisphenol A (BPA). The Bi2O3-ZnO heterostructure nanocomposite was found to be a more effective photocatalyst than Bi2WO6. The effect of operating parameters including catalytic dose (0.02-0.15 gL-1), initial BPA concentration (5-20 mgL-1), temperature change (5-20 °C) and solution pH changes (4, 5, 7, and 8) were evaluated with Bi2O3-ZnO under UV-light irradiation by selecting a 300 W Xe lamp. More than 90% BPA was degraded with 0.15 gL-1 Bi2O3-ZnO, keeping 1.0 mM H2O2concentration fixed in 250 mL of reaction suspension. The HPLC and GC-MS were used to detect the reaction intermediates and final products. A plausible degradation pathway was proposed on the basis of the identification of reaction intermediates. Repeatability test analysis confirmed that the as-synthesized catalyst showed superb catalytic performance on its removal trend. The kinetics of degradation of BPA were well fitted by the power laws model. With the order of reaction being 0.6, 0.9, 1.2, and 1.3 for different operating parameters, i.e., catalyst dose, initial pH, temperature, and initial BPA concentration.

Coal fly ash supported ZnO catalyzed transesterification of Jatropha curcas oil: Optimization by response surface methodology

• Biodiesel was produced via transesterification of JCO by Coal fly ash supported ZnO (ZnO-CFA). • Activity of ZnO-CFA catalyst was enhanced by calcination at 400 o C. • Under the optimal transesterification conditions, maximum biodiesel yield was 91.08 ± 0.06%. • Physicochemical properties of produced biodiesel agreed with ASTM D6751 and EN 14214 . Herein, a zinc oxide based coal fly ash (ZnO-CFA) composite as heterogeneous catalyst was formulated and explored for transesterification of non-edible oil (Jatropha curcas oil, JCO). The as-synthesized catalyst was analyzed to gain insights into its properties using various characterization techniques (EDX, FTIR, TEM, XRD and BET surface area). The solid catalyst’s ability to catalyze the methanolysis reaction was investigated and optimized at varying reaction temperature, methanol/JCO molar ratio and catalyst dosage using Box-Behnken design. Predicted value of biodiesel yield was found to be in excellent agreement with observed value with high coefficient of determination R 2 = 0.9759 a n d A d j . R 2 = 0.9449 . It was determined that optimum transesterification process conditions of 60.4 o C reaction temperature, 11.8:1 methanol/JCO molar ratio and 1.63 wt.% catalyst loading resulted in biodiesel yield and FAME content of 91.08 ± 0.06% and 97.22%, respectively. Additionally, the produced biodiesel at the optimum conditions was shown to be conformed to ASTM standard. The ZnO-CFA catalyst was simple to synthesize and handle, eliminating the need for costly aluminosilicate-based catalysts in biofuel synthesis. It was also simple to separate from the product stream and could be recycled up to four times.

TiC-Supported ruthenium nanoparticles as an efficient electrocatalyst for the hydrogen evolution reaction

The indiscreet use of fossil fuels has led to environmental pollution. To mitigate this, it is expected that the hydrogen evolution reaction (HER) can be performed at the cathode of electrolytic cells in energy conversion devices and eco-friendly renewable energy sources. Owing to the sluggish kinetics of the HER, the design and development of cost-effective, long term, highly stable, and efficient alternative electrocatalysts are crucial for their practical application. Herein, ruthenium (Ru) particles loaded titanium carbide (Ru/TiC) are successfully prepared through a simple reduction method. We employ experimental approaches to investigate the stability and electrocatalytic activity of Ru as a transition metal atom on a TiC support. The as-synthesized catalyst is characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Ru/TiC electrocatalyst exhibits HER activity with low overpotentials, fast reaction kinetics and high stability in alkaline and acidic medium. The remarkable electrocatalytic activity of Ru/TiC will promote interest in the futuristic development of cost-effective nanomaterials for energy and environmental applications.

Highly dispersed iron/nickel dual-sites in hierarchical porous carbon materials as high-performance bifunctional oxygen electrocatalysts for Zn-air batteries

Designing non-precious metal electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) not only should improve the activity of the catalytic reaction sites, but also need to consider the transport channels of the reactants and electrolyte inside the catalysts to enhance the utilization of active sites. Here, Fe/Ni dual-active sites anchored on the unique honeycomb hierarchical porous carbon materials are successfully prepared by pyrolysis of Fe and Ni bimetal co-doped covalent organic polymer with the assistance of pore-forming agents. The unique honeycomb hierarchical porous structures are favorable for transport and diffusion of oxygen and electrolyte during the electrochemical reaction process, so that the internal active sites can be fully utilized to improve the catalytic activity. The as-synthesized catalyst exhibits excellent ORR (E1/2 = 874 mV) and OER (overpotential = 352 mV at 10 mA cm−2) performance. More importantly, the rechargeable liquid Zn-air battery assembled with the catalyst exhibits a large specific capacity of 781.7 mA h g−1 and a long-term cycle stability with repeatedly charging and discharging for 450 h at 20 mA cm−2. Additionally, an all-solid-state flexible Zn-air battery based on this catalyst as cathode shows a maximum power density of 83.5 mW cm−2.

Atomization driven crystalline nanocarbon based single-atom catalysts for superior oxygen electroreduction

Atom-migration-trapping (AMT) is an effective and straightforward strategy for fabricating single-atom catalysts (SACs), but understanding the mechanism and effects of anchoring sites on AMT are formidable challenges. Here, we demonstrate that AMT phenomena occurs in crystalline porous nanocarbon, which allows development of highly efficient SACs via systematic investigation of atomization process and chemical state of active sites. An arc discharge-based bottom-up synthesis can generate an ideal porous nanocarbon with controllable nitrogen functionality, containing metal nanoparticles for AMT. Pre-formed N-functionalities in as-synthesized catalyst play important role in capturing single metal species, while additional ammonia treatment successfully modulates coordination geometry of active sites. The atomic cobalt catalyst exhibits superior oxygen reduction activity with remarkable power performance in single-cell experiments (752 mW cm−2), exceeding the reported Co-N atomic catalysts. Our findings provide not only new perspectives in AMT phenomena but also strategies to develop an efficient and practical SACs in energy conversion systems.

Using ammonia solution to fabricate highly active Au/ uncalcined TS‑1 catalyst for gas-phase epoxidation of propylene

Reducing the Au particle size and increasing the number of defective Ti4+ species have been considered effective strategies to boost the catalytic performance of Au–Ti bifunctional catalysts used for propylene epoxidation utilizing H2 and O2. Consequently, the development of an effective method that can simultaneously achieve these goals is of significant scientific and industrial importance. Herein, we demonstrate, for the first time, that the simultaneous immobilization of small Au particles (approximately 1.6 nm) onto uncalcined titanium silicate-1 (i.e., TS-1-B) and facilitation of the formation of defective Ti4+ species can be achieved using a modified deposition–precipitation (DP) method utilizing ammonia solution as the precipitant. The as-synthesized catalyst exhibits a significantly enhanced propylene oxide (PO) formation rate combined with fascinating PO selectivity and hydrogen efficiency, which were better than the reference catalyst prepared via the DP urea (DPU) method and other reported Au/uncalcined TS-1 catalysts. The catalyst structure–performance relationship was established using multiple characterization studies. the ammonia treatment facilitates the hydrolysis of some of the ≡Ti-O-Si≡ bonds into defective Ti4+ species (i.e., Ti(OSi)3OH), which not only provides more active Ti4+ sites but also favors the uniform deposition of Au. This methodology and the insights stated herein may also be applicable for enhancing the dispersion of Au in a variety of zeolite-supported catalysts.

Selective hydroxylation of benzene to phenol via C[sbnd]H activation over mesoporous Fe2O3-TiO2 using H2O2

The omnipresence of CH bonds in organic molecules enamors chemists for the functionalization of CH bonds towards value-added molecular scaffolds. Mesoporous Fe2O3-TiO2 mix-oxide catalyst has been successfully synthesized via a triblock-copolymer (P123) mediated sol-gel method and catalytically tested in selective hydroxylation of benzene. The as-synthesized catalysts were comprehensively characterized by powder XRD, Raman spectroscopy, FT-IR, N2-physisorption, FESEM, HRTEM, XPS, and NH3-TPD techniques. The physicochemical characterizations evidence that Fe(III) ions incorporate into the pure anatase TiO2 lattice framework and the crystallite size decreases as iron concentration increases. The XPS analyses confirm the Fe3+ state (BE 710.3 eV) in Fe-O-Ti with a peak at 712.1 eV for Fe3+ of Fe2O3. The NH3-TPD results show that the 5 wt% Fe-TiO2 has a higher total acidity of 105 µmol/g. Interestingly, a further increase in iron amount decreases the total acidity. Herein, we observe that the surface acidity directs the selectivity towards phenol. The effect of different reaction parameters was carefully investigated. Under the optimized conditions, 5% Fe-TiO2 with notified strong acid sites gives a higher phenol yield of 31.2% with > 99% selectivity; moreover, the catalyst is reusable at least four times.

Drastically enhanced tetracycline degradation performance of a porous 2D g-C3N4 nanosheet photocatalyst in real water matrix: Influencing factors and mechanism insight

Porous 2D nanosheets are an emerging class of materials with exciting physical, chemical, optical, and electronic characteristics. This study reported the facile synthesis of a porous 2D g-C3N4 nanosheet photocatalyst through a simple chemical exfoliation route. The morphological characterization of the samples confirmed its porous 2D nanosheet structure with an approximate thickness of 2.5 nm. The as-prepared photocatalyst displayed a 4.2-fold enhanced tetracycline (TC) degradation rate coefficient compared to the pristine g-C3N4 under LED illumination. Further, the porous 2D g-C3N4 nanosheet photocatalyst exhibited superior TC degradation efficacy in a real water matrix. The synergistic effect of higher pH, presence of carbonate and bicarbonate anions, and the existence of humic substances could have elevated the degradation performance in the real water matrix. Moreover, the as-synthesized catalyst demonstrated remarkable stability and recyclability even after the four-cycle recycling experiment. A possible photocatalytic mechanism has been proposed following the findings of the radical trapping experiment. It is believed that this study would inspire further fabrication of other porous 2D nanosheet photocatalysts.

Chalcogenic heterostructure supported on carbon nanostructure for electrochemical water dissociation

The development of an efficient and stable non-noble metal catalyst to replace noble metal catalyst for hydrogen evolution reaction (HER) is still a challenge. Herein, we report one-step hydrothermal method to synthesis binary hybrid material composed of MoS2/CoS2 heterostructure (HS) supported on reduced graphene oxide (rGO). The coexistence of HS and rGO exhibit lower overpotential towards the HER activity with superior structural stability comparing to MoS2, CoS2 and MoS2/CoS2 under acidic condition. The MoS2/CoS2@rGO yielded a low overpotential of −152 mV at cathodic current density −10 mAcm−2 compared to MoS2, CoS2 and MoS2/CoS2 with values of −322 mV, −537 mV and −238 mV. Also, a low Tafel slope value of MoS2/CoS2@rGO (65 mVdec−1) reflects its superior performance compared to other as-synthesized catalysts. The superior activity of MoS2/CoS2@rGO attributed by conductive support of rGO and strong interaction between HS and water molecule. The avenues of active sites were triggered due to the formation of HS and electrical conductivity enhancement occurred due to the presence of carbon nanostructure, which proves that further engineering of the catalyst can reduce the overpotential drastically.

Metal-Organic framework derived CuCo2O4 as a promising Co-Catalyst for improving electrochemical hydrogen evolution activity of MoS2 nanoflowers

The great promise of electrochemical water splitting for green and sustainable hydrogen fuel production has motivated researchers to strive for more efficient and low-cost catalysts based on non-precious metals. In this study, MoS2 nanoflowers decorated with CuCo2O4 were successfully synthesized, and their catalytic activities toward the electrochemical hydrogen evolution reaction (HER) in an alkaline medium were investigated. The composition, structure, and morphology of the as-synthesized catalysts were explored by various techniques such as FT-IR, XRD, BET, SEM, and TEM. To maximize the catalytic activity, the composition of the nanocomposites was systematically varied. Catalytic results revealed that catalyst with the 90:10 mass ratio of CuCo2O4 to MoS2 (NC-90:10) demonstrated the best HER efficiency, with a measured overpotential of 237 mV (at the current density of 20 mA cm−2) and a Tafel slope of 134 mV dec−1. Furtheremore, NC-90:10 showed graet long-term stability.

Facile synthesis of NdFeO3 perovskite for photocatalytic degradation of organic dye and antibiotic

In this study, a visible-light sensitive neodymium iron oxide (NdFeO3) perovskite nanostructure was fabricated via facile citrate sol–gel method to target the degradation of lomefloxacin (LMF) antibiotic and methylene blue (MB) dye. The as-synthesized catalyst were investigated employing various characterization techniques scuch as XRD, EDX, SEM, UV–vis and PL. The NdFeO3 photocatalyst demonstrates excellent photocatalytic activity of maximum 88 % and 95 % for the photodegradation of LMF (15 mg/L) and MB (15 mg/L) in 120 min under a visible light source (LED, 30 W). The current study provides an exciting technique for developing a NdFeO3 photocatalyst capable of high-performance LMF and MB detoxification.

Hydrothermal synthesis of chalcostibite nanoflowers with enhanced visible light photocatalytic activity

A novel visible-light-driven CuSbS2 nanoflowers (CAS-NFs) catalysts were successfully synthesized through a low-cost and easy hydrothermal method. The unique point of our work is to investigate the photocatalytic activities of the synthesized catalysts and their use for environmental remediation. The as-synthesized CuSbS2 catalysts were carefully characterized by scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, and diffuse reflectance spectroscopy tools. Stoichiometric CAS-NFs were achieved for hydrothermal reaction temperature 150 °C and reaction time closer to 15 h. To check the photocatalytic activity of CAS-NFs, we have used two wastewater dyes, namely, methyl orange and rhodamine B under visible light irradiation. The results indicate that rhodamine B presented higher photocatalytic degradation as compared to methyl orange. Furthermore, the photodegradation rate over five sequential cycles as well as scavenging studies has been scrutinized for RhB dye under visible light. The results indicate its outstanding stability and reusability. Based on the results of radical’s scavenger experiments, we demonstrate that h+ and (•OH) radicals are the main reactive species. Lastly, a judicious mechanism was suggested to demonstrate the photocatalytic degradation process by the CAS-NFs for rhodamine B dye under Xe-lamp irradiation.

Ni3C MXene nanosheets as an efficient binder-less electrocatalyst for oxygen evolution reaction

Low overpotential driven water-splitting is globally proposed as an effective replacement of conventional energy generation devices. However, these applications are extensively reported with noble electrocatalysts which makes them unsuitable for large scale applications. Therefore, it is essential to develop a non-noble, highly stable and low-cost electrocatalyst for oxygen evolution reaction (OER). In this report, we demonstrate solvothermal HF free etching and exfoliation of Ni-MAX to form Ni-MXene nanosheets as an effective electrocatalyst for OER. The as-synthesized Ni-MXene catalyst over nickel foam NiMX/NF electrode exhibits an overpotential of 245 mV at 100 mA/cm2. This performance can be attributed to the increased electrocatalytic activity and enhanced conductivity of the catalyst due to the presence of Ni2+/3+ redox couple and carbon in the Ni-MXene nanosheets, respectively. The catalyst electrode exhibits 83 % of current density retention after 14 h of continuous catalysis. This proves Ni MXene as an ideal candidate for the large scale and industrial applications of OER.

Enhanced Photocatalytic Degradation of Amoxicillin with Mn-Doped Cu2O under Sunlight Irradiation

In this work, we report the synthesis of Mn-doped Cu2O nanoparticles using aloe vera leaves extract. X-ray diffraction data revealed that the Mn-doped Cu2O crystals have a cubic crystal structure. The surface morphology of the as-synthesized catalyst indicated truncated octahedral and spherical-like shapes. The photocatalytic activity of the catalyst is efficient at pH 9, initial concentration of amoxicillin 15 mg/L, and photocatalyst dosage 1 g/L under sunlight irradiation. 92% of amoxicillin was degraded in the presence of Mn-doped Cu2O. The enhancement in photocatalytic performance is due to the incorporation of Mn, which delays the rapid recombination rate by trapping the photogenerated electron. Therefore, Mn-doped Cu2O could remove pharmaceuticals from pharmaceutical factory and hospital wastes.

Catalytic performance of calcined Fe2O3/CA catalyst for NH3-SCR reaction: Role of activation temperature

With the purpose of developing an environment-friendly and high-efficiency catalyst for the selective catalytic reduction of nitrogen oxides (NOx) by ammonia (NH3-SCR), citric acid (CA)-decorated Fe2O3 (Fe2O3/CA) was synthesized via a simple water bath method and followed by calcination activation. The catalytic performance showed that the catalyst activity was closely related to the calcination temperature. When the calcination temperature was 300 ​°C, the as-synthesized catalyst displayed the best NH3-SCR activity, and extraordinary N2 and N2O selectivity in a wide range of operating temperatures. Subsequently, the crystal phase, morphology, physical features, chemical states, redox properties, and surface acidity properties of the as-synthesized catalysts were investigated by various characterization techniques. The results demonstrated that Fe2O3/CA calcined at a suitable temperature could promote the speciation transformation of the partial phase from α-Fe2O3 to γ-Fe2O3. In addition, appropriate calcination of Fe2O3/CA could also improve the reducibility and increase the number of acid sites. All of these factors, collectively, accounted for the excellent NH3-SCR activities of the catalyst.

High-entropy alloy anode for direct internal steam reforming of methane in SOFC

High-entropy alloy (HEA) anode and reforming catalyst, supported on gadolinium-doped ceria (GDC), have been synthesized and evaluated for the steam reforming of methane under SOFC operating conditions using a conventional fixed-bed catalytic reactor. As-synthesized HEA catalysts were subjected to various characterization techniques including N2 adsorption/desorption analysis, SEM, XRD, TPR, TPO and TPD. The catalytic performance was evaluated in a quartz tube reactor over a temperature range of 700–800 °C, pressure of 1 atm, gas hourly space velocity (GHSV) of 45,000 h−1 and steam-to-carbon (S/C) ratio of 2. The conversion and H2 yield were calculated and compared. HEA/GDC exhibited a lower conversion rate than those of Ni/YSZ and Ni/GDC at 700 °C, but showed superior stability without any sign of carbon deposition unlike Ni base catalyst. HEA/GDC was further evaluated as an anode in a SOFC test, which showed high electrochemical stability with a comparable current density obtained on Ni electrode. The SOFC reported low and stable electrode polarization. Post-test analysis of the cell showed the absence of carbon at and within the electrode. It is suggested that HEA/GDC exhibits inherent robustness, good carbon tolerance and stable catalytic activity,` which makes it a potential anode candidate for direct utilization of hydrocarbon fuels in SOFC applications.

Tailoring the surface wettability of mesoporous silica for selective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde in a Pickering emulsion system

The development of facile and reliable protocols for the functionalization of mesoporous silica particles is an essential aspect in the field of nanomaterials. We reported the use of co-condensation to methodically tune the surface wettability of mesoporous silica particles, using a mixture of (3-aminopropyl) triethoxysilane, tetraethyl orthosilicate and methyltrimethoxysilane. Pd nanoparticles were deposited on the series of interfacial active mesoporous silica particles using the wet impregnation method, and the as-synthesized catalysts were used as stabilizers and efficient catalysts for the selective hydrogenation of cinnamaldehyde in the Pickering emulsion system under static conditions. The catalytic activity of cinnamaldehyde was greatly influenced by surface wettability and concentration of the mesoporous structured catalysts. Interestingly, the PE system shows above 90% selectivity to HCAL over Pd/MS-MAP15 catalyst, moreover, the Pd/MS-MAP15 is highly recyclable after eight consecutive reaction runs. This is a significant advancement in material science and interfacial catalysis with industrial relevance.

Photoinduced CO2 and N2 reductions on plasmonically enabled gallium oxide

Ag-containing ZnO/ β-Ga2O3 semiconductor, which exhibit reduced bandgap, increased light absorption, and hydrophilicity, have been found to be useful for photocatalytic CO2 reduction and N2 fixation by water. The charge-separation is facilitated by the new interfaces and inherent vacancies. The Ag@GaZn demonstrated the highest photocurrent response, about 20- and 2.27-folds that of the Ga and GaZn samples, respectively. CO, CH4, and H2 formed as products for photo-reduction of CO2. Ag@GaZn catalyst exhibited the highest AQY of 0.121 % at 400 nm (31.2 W/m2). Also, Ag@GaZn generated 740 μmolg-1 of NH4+ ions, which was about 18-folds higher than Ga sample. In situ DRIFTS for isotopic-labelled 13CO2 and 15N2 reaffirmed the photo-activity of as-synthesized catalysts. Density functional theory provided insight into the relative affinity of different planes of heterostructures towards H2O, CO2 and N2 molecules. The structure-photoactivity rationale behind the intriguing Ag@GaZn sample offers a fundamental insight into the role of plasmonic Ag and design principle of heterostructure with improved photoactivity and stability.