Metal-doped SnO2 Research Articles

Electronic structure modification of SnO2 to accelerate CO2 reduction towards formate.

A systematic theoretical study probing the catalytic potential of metal-doped SnO2(110) was conducted. The incorporation of metals such as Zr, Ti, W, V, Hf, and Ge is shown to drive electron transfer to Sn. The increased charge of Sn is injected into anti-bonding orbitals, finely tuning the catalytic activity and reducing the overpotential to -0.34 V. AIMD simulations show the stability of the modified structures. This work sheds light on the rational design of low-cost metal oxides with a high catalytic performance for CO2ER to formate.

Enhanced dopant incorporation into SnO2 thin films based on dual source spray pyrolysis deposition process

Recently, SnO2 has attracted much attention for optoelectronic applications in infrared (IR) spectral ranges due to its high transparency in the ultraviolet to IR wavelength spectral range and high electrical conductivity. The transition metal-doped SnO2 based on the ultrasonic-assisted spray pyrolysis deposition (SPD) method has been widely used for various optoelectronic applications. However, the SPD process has suffered from inefficient doping of foreign elements due to difficulties in controlling the single precursor source solutions and complicated solution dynamics. To overcome these problems, the co-SPD process supplying the host and dopant solutions separately was suggested for the deposition of the Zn-doped SnO2 thin films. The Zn-doped SnO2 thin films deposited by co-SPD showed insulating electrical properties due to the efficient incorporation of the Zn element as an oxygen vacancy scavenger and acceptor to annihilate the free charge carriers. Also, the Zn-doped SnO2 films showed an IR transmittance of over 80 %, maintained at a temperature of up to 500 ℃. Thus, the co-SPD process can be a promising approach to achieve highly doped oxide films with high IR transmittance even at elevated temperatures.

A novel detection method for sulfur content in ship fuel based on metal-doped tin oxide quantum dots as fluorescent sensor

The International Maritime Organization (IMO) issues compulsory regulations that require fuel sulfur content (FSC) less than 0.50% (m/m) to reduce sulfur dioxide emission from ships. However, current FSC detection suffers from low efficiency and high cost. In this work, a novel method for FSC detection is developed based on semiconductor quantum dots (QDs). The adsorption properties of primary functional groups -SH, –COOH, –NH2, –OH, and –CN of organic compounds in fuel on pristine and metal-doped tin oxide (SnO2) QDs are simulated by density functional theory (DFT) calculations. Ni dopant is selected after screening adsorption of organics on metal-doped SnO2. The fluorescent sensor is designed by nickel-doped SnO2 (Ni-SnO2) QDs for the FSC detection. The detection range and limit of detection are 0.429–0.97% m/m and 0.065% m/m, respectively. Furthermore, the sensing mechanism is discussed and the quenching of fluorescence emission of Ni-SnO2 QDs is ascribed to the photoinduced electron transfer. This work provides a novel technique based on Ni-doped SnO2 QDs for actual fast-responsive, highly-selective, reliably-repeatable, low-cost FSC detection, which can meet the detection requirements of FSC below 0.10% m/m in the emission control areas (ECAs).

A computational study of electrochemical CO2 reduction to formic acid on metal-doped SnO2

Electrochemical reduction of CO2 to formic acid (HCOOH) can contribute to the renewable energy transition as a liquid carrier of renewably hydrogen. Here, we investigated the catalytic requirements of SnO2 electrodes for efficient CO2 reduction to HCOOH using density functional theory and microkinetics simulations. Hydroxylation of the surface is a prerequisite to achieve a high activity with predicted current densities in agreement with experiment. The resulting surface is selective to HCOOH production with a negligible contribution of the hydrogen evolution reaction. Mechanistically, it is found that the reaction proceeds via hydrogenation of adsorbed CO2 to carboxylate (COOH), which is then further hydrogenated to the desired product. Doping of the surface by commonly used elements (Bi, Pd, Ni and Cu) identifies Bi as the preferred promoter to substantially improve the current density. Brønsted-Evans-Polanyi relations are established for the two key steps in the mechanism. Overall, carboxylate formation is the rate-controlling step. The CO2 reduction activity is analyzed in terms of two descriptors, namely the free energies for the two protonation steps, showing that Bi presents the highest activity.

Transition metal elements-doped SnO2 for ultrasensitive and rapid ppb-level formaldehyde sensing

Pristine SnO2, Fe-doped SnO2 and Ni-doped SnO2 were synthesized using facile hydrothermal method. Analysis based on XRD, TEM and UV–Vis DRS measurements demonstrated the successful insertion of Fe and Ni dopants into SnO2 crystal. Formaldehyde-detection measurements revealed that transition metal-doped SnO2 exhibited improved formaldehyde-sensing properties compared with that of pristine SnO2. When the amount of incorporated dopant (Fe or Ni) was 4 at.%, the most effective enhancement on sensing performance of SnO2 was obtained. At 160 °C, the 4 at.% Fe–SnO2 and 4 at.% Ni–SnO2 exhibited higher response values of 7.52 and 4.37 with exposure to low-concentration formaldehyde, respectively, which were 2.4 and 1.4 times higher than that of pristine SnO2. The change of electronic structure and crystal structure as well as catalytic effect of transition metals are chiefly responsible for the enhanced sensing properties.

Transition metal-doped SnO2 and graphene oxide (GO) supported nanocomposites as efficient photocatalysts and antibacterial agents.

In the present work, pristine and transition metal (TM) (W, Ag, Zn)-doped SnO2 nanocrystals using a facile sol-gel approach were synthesized. The grown products were anchored on graphene oxide (GO) sheets via a simple ultrasonication technique to fabricate binary nanocomposites. The structural, optical, and morphological properties of as-synthesized samples were studied by XRD, FTIR, Raman, EDX, UV-Visible, PL, and FE-SEM. The charge transferability of graphene oxide-based samples was investigated by EIS. The XRD exhibited the TM doping in SnO2 and the development of GO-based nanocomposite. FTIR data evidenced the existence of the metal-oxygen bonds. Raman spectra presented the optical phonon modes of SnO2 and the existence of oxygen vacancy defects. FE-SEM images demonstrated the anchoring of particles on the GO sheet, and EDX further approved the existence of desired dopants. The integration of SnO2 with TM doping remarkably reduced optical bandgap (3.65-3.10eV), which was further decreased (3.10-2.99eV) by making composite with GO. The photodegradation results exhibited that GO-based nanocomposites have the higher potential to degrade synthetic dyes (methyl red (MR), and methyl orange (MO) and SnZnO2/GO have shown superb photocatalytic performance after 80-min sunlight illumination (99.9% MR and 95.0% MO dyes) with the higher rate constant and superior stability up to 6th cycle against MR dye. The grown samples were tested for bacterial disinfection, and SnZnO2/GO sample showed a higher zone of inhibition towards S. aureus and K. pneumoniae bacteria strains. The greater charge transfer rate and lower recombination of charge carriers in GO-based composites were also observed by EIS and PL analysis. Moreover, the present article ascribed that the photocatalytic and antibacterial properties of bare SnO2 could be improved by TM doping and fabricating their composite with GO.

Solution-processed metal doping of sub-3 nm SnO2 quantum wires for enhanced H2S sensing at low temperature

Sub-3 nm metal-doped SnO2 quantum wires (QWs) were synthesized using a solution process. The sensor film prepared using W-doped SnO2 QWs at room temperature achieves enhanced low-temperature H2S-sensing with a record limit of detection of 0.48 ppb.

Electrochemical studies on doped SnO2 nanocomposite for selective detection of lung cancer biomarkers

Lung cancer (LC) is one of the major disease causes for cancer-related mortality. The detection of volatile organic compounds (VOCs) as lung cancer biomarkers will be useful for early stage detection. Hence, the development of electrochemical sensors to detect acetone and toluene as biomarkers below the allowed permissible limit in a sensitive and selective manner is essential. In this study, transition metal ion doped SnO2 nanocomposites have been developed by the hydrothermal method and used for the selective detection of LC biomarkers. The morphologies, structures, and chemical compositions of synthesized materials were studied using field-emission scanning electron microscopy (FESEM), x-ray diffraction, UV–visible spectroscopy, and Fourier transform infrared spectroscopy. The UV–visible study revealed that the doping of metal ions reduces the bandgap, and FESEM analysis showed a spherical like morphology that improves the adsorption sites on materials. Furthermore, cyclic voltammetry and electrochemical impedance spectroscopy revealed that the doping of transition metal ions improves the charge transfer ability and electrochemical activity of nanocomposites. The selective chemisorption of lung cancer biomarkers on metal-doped SnO2 nanocomposites helps in achieving a superior response with a broad linear detection range (20–100 ppb for toluene and 1–1000 ppb for acetone). In addition, the limit of detection achieved for toluene (1 ppb) and acetone (0.1 ppb) is well below the permissible limit for lung cancer patients. The fabricated nanocomposite is found to be highly selective toward acetone and toluene with a selectivity factor ranging from 1.8 to 12 and 6.6 to 10, respectively, as compared with other VOCs.

CO2 reduction on metal-doped SnO2(110) surface catalysts: Manipulating the product by changing the ratio of Sn:O

The electrocatalytic carbon dioxide reduction reaction (CO2RR) producing HCOOH and CO is one of the most promising approaches for storing renewable electricity as chemical energy in fuels. SnO2 is a good catalyst for CO2-to-HCOOH or CO2-to-CO conversion, with different crystal planes participating the catalytic process. Among them, (110) surface SnO2 is very stable and easy to synthesisze. By changing the ratio of Sn:O for SnO2(110), we have two typical SnO2 thin films: fully oxidized (stoichiometric) and partially reduced. In this work, we are concerned with different metals (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au)-doped SnO2(110) with different activity and selectivity for CO2RR. All these changes are manipulated by adjusting the ratio of Sn:O in (110) surface. The results show that stochiometric and reduced Cu/Ag doped SnO2(110) have different selectivity for CO2RR. More specifically, stochiometric Cu/Ag-doped SnO2(110) tends to generate CO(g). Meanwhile, the reduced surface tends to generate HCOOH(g). Moreover, we also considered the competitive hydrogen evolution reaction (HER). The catalysts SnO2(110) doped by Ru, Rh, Pd, Os, Ir, and Pt have high activity for HER, and others are good catalysts for CO2RR.

Electrocatalytic activity of metal-doped SnO2 for the decomposition of aqueous contaminants: Ta-SnO2 vs. Sb-SnO2

Sb-doped SnO2 (ATO) is one of the most widely used electrocatalyst anodes for the oxidation of water and wastewater. This study synthesizes Ta(V)-doped SnO2 (TTO) electrocatalysts as alternatives to ATO and systematically examines their electrocatalytic activity for the decomposition of organic substrates in various electrolyte solutions. The as-synthesized TTO exhibits the highest activity for the decomposition of phenol, N,N′-dimethyl-4-nitrosoaniline, and rhodamine-B at a Ta doping level of ~1%. The optimized TTO exhibits a higher activity for the decomposition of phenol than ATO in a chloride solution and a lower activity than ATO in a sulfate solution. Electron paramagnetic resonance analysis reveals that a relatively larger production of reactive oxygen species is achieved with ATO, whereas a larger production of reactive chlorine species is obtained with TTO. In the durability tests, both electrodes favor an alkaline condition (pH 12.8) over acidic and neutral conditions (pH 1.5 and 6.2, respectively), and Ta-SnO2 is less stable than Sb-SnO2 over the full pH range. Additionally, solid-state and electrochemical surface characterizations are carried out.

Improved photocatalytic performance of nanostructured SnO2 via addition of alkaline earth metals (Ba2+, Ca2+ and Mg2+) under visible light irradiation

Pure and alkaline earth metal (Ba2+, Ca2+ and Mg2+)-doped tin oxide nanoparticles were synthesized by simple co-precipitation, and their structural, optical, functional, morphological and compositional properties were analyzed in detail using powder X-ray diffraction, UV–visible spectroscopy, photoluminescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy and energy-dispersive analysis of X-ray (EDAX). XRD revealed the formation of rutile tetragonal structure, and the crystallite size has decreased from 28 to 24 nm by the addition of alkaline metal dopants. FTIR spectra confirmed the presence of fundamental vibration modes of SnO2. The optical band gap energy was decreased to 3.05, 3.19 and 2.98 eV by introducing Ba2+, Ca2+ and Mg2+ ions, respectively. Photoluminescence spectra showed defect-related emission peaks, and their intensities were found to increase in doped SnO2 samples. EDAX spectra confirmed the presence of Sn, O, Ba, Ca and Mg elements. The photocatalytic activity of pure and alkaline metal-doped SnO2 catalyst has been investigated under visible light irradiation by using methylene blue dye. The results showed that the Mg-doped SnO2 catalyst has a higher photodegradation efficiency (~ 95.7%) compared with other investigated samples.

Transition metal doped Sb@SnO2 nanoparticles for photochemical and electrochemical oxidation of cysteine

Transition metal-doped SnO2 nanoparticles (TM-SnO2) were synthesized by applying a thermos-synthesis method, which first involved doping SnO2 with Sb and then with transition metals (TM = Cr, Mn, Fe, or Co) of various concentrations to enhance a catalytic effect of SnO2. The doped particles were then analyzed by using various surface analysis techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning transmission X-ray microscopy (STXM), and high-resolution photoemission spectroscopy (HRPES). We evaluated the catalytic effects of these doped particles on the oxidation of L-cysteine (Cys) in aqueous solution by taking electrochemical measurements and on the photocatalytic oxidation of Cys by using HRPES under UV illumination. Through the spectral analysis, we found that the Cr- and Mn-doped SnO2 nanoparticles exhibit enhanced catalytic activities, which according to the various surface analyses were due to the effects of the sizes of the particles and electronegativity differences between the dopant metal and SnO2.

The effect of oxygen vacancies on the hyperfine properties of metal-doped SnO2

We have performed a Mössbauer investigation of oxygen-vacancy formation on a doped substitutional solution of Sn1−yMyO2 (M = Al, Fe, Ce and Er) nanoparticles. Experimental results were assessed from Mössbauer spectroscopy data, which suggest the rise of the oxygen-vacancy population while increasing the content of dopant ions (M). Likewise, we have analyzed the dependence of the structural, electronic and hyperfine properties on the oxygen-vacancy concentration through first-principles calculations of the SnO2−x (where x varies from 0 to 0.25) system. The results obtained from the isomer shift and quadrupole splitting indicate a significant dependence of the hyperfine properties on the number of oxygen vacancies. Moreover, after structural optimization of the Sn16O32-Vo supercell (where Vo is the number of oxygen vacancies) we found an increase of the unit-cell volume with the increase of Vo, while the bulk modulus showed a linear decrease with Vo. Indeed, our results corroborate the experimental findings for pure and transition-metal-doped SnO2 systems for which the presence of the oxygen vacancy plays a key role.

Ethanol Response of Semiconductor Gas Sensors Based on SnO2 Layer Prepared from Acidic Solution

We examined the response behavior of SnO2 based semiconductor gas sensors to ethanol. In this study, the sensing layer was fabricated from mixed solutions of tin acidic standard solution with zinc or titanium acidic standard solution. The sensitivity of SnO2 sensors prepared from acidic standard solutions to ethanol was higher than that of metal-doped SnO2 sensors prepared from SnO2 powders. The sensitivity of Zn-doped SnO2 sensors was depressed in the humidified environment, while the sensitivity of Ti-doped SnO2 sensors was not affected by humidity even if the relative humidity was high. SnO2 films prepared from SnO2 powders composed of particles with 100 nm mean particle diameter. By using tin standard solution as a material of film, semiconductor films formed of fine particles having 10 nm mean particle diameter was obtained. This film formation method using acidic standard solutions can control the thickness of film easy, and the thin SnO2 film with around 100 nm thickness could be obtained.

Simultaneous removal of COS and H2S from hot syngas by rare earth metal-doped SnO2 sorbents

The pure SnO2 and rare earth metal (Y and La)-doped SnO2 were synthesized using a co-precipitation method for the simultaneous removal of COS and H2S from hot syngas at 350°C. The pure SnO2 sorbent exhibited a poor catalytic hydrolysis effect for COS conversion at moderate temperatures of 300–400°C due to the formation of SnS during the desulfurization. SnS caused a decrease in the COS conversion because the activity of SnS was considerably lower than that of reduced SnO2 for the hydrolysis of COS. The addition of Y and La resulted in the formation of numerous smaller pores and increased the total pore volume of the sorbents. The good dispersion of rare earth metal resulted in the improvement of COS conversion, which produced a higher breakthrough sulfur capacity. As the La content increased, the COS conversion reached nearly 100% and was no longer the restrictive procedure for the simultaneous removal of COS and H2S. The total breakthrough sulfur capacity was 148.4mg/g when 40M percent of La was doped into the SnO2 sorbent.

Ecofriendly synthesis of ultra-small metal-doped SnO2 quantum dots

Abstract

Development of Metal-Doped SnO2 Electrodes for Electrocatalytic Water Treatment

not Available.

Defect chemistry in ruthenium-supported tin dioxide: a spectromagnetic approach

The reactivity towards CO and air of SnO2 defects, singly and doubly ionized oxygen vacancies (Vo⋅ Vo⋅⋅), bivalent tin centers, was studied in ruthenium-supported tin oxide (Ru/SnO2), and compared with that in pure SnO2. Electron paramagnetic resonance and X-ray photoelectron spectroscopy studies demonstrated that CO treatment produces Vo⋅ and Vo⋅⋅ defects in SnO2, some Vo⋅ transferring their electrons to Sn4+centers; instead in Ru/SnO2, some Vo⋅ defects transferred their electrons to Run+centers (n=0,1,2,3) and no one bivalent tin center was observed. When contacted with air, pure SnO2 transferred a part of the electrons of Vo⋅ and of bivalent tin centers to O2, instead Ru/SnO2 emptied all Vo⋅ defects transferring the electrons from Vo⋅ to ruthenium and to O2. The via ruthenium transfer increases the number of electrons exchanged between SnO2 and the surrounding atmosphere and gave a rationale for the higher sensitivity towards CO displayed by transition metal-doped SnO2 with respect to pure SnO2.

FOREIGN METAL-DOPED SnO2 FILM ANODES FOR OXYGEN AND CHLORINE EVOLUTION

Abstract The anodic characteristics of foreign metal-doped SnO2 film electrodes, prepared by the thermal decomposition method, were studied in 1M KOH and 3M NaCl solutions. As a result, it was found that such electrodes have very attractive properties as anodes for oxygen and chlorine evolution.