Next Article in Journal
Characterization and Applications of Metal Ferrite Nanocomposites
Next Article in Special Issue
Controlled Deposition of Nanostructured Hierarchical TiO2 Thin Films by Low Pressure Supersonic Plasma Jets
Previous Article in Journal
Nanoplasmonic Strip Test for Salivary Glucose Monitoring
Previous Article in Special Issue
Improvement of Nanostructured Polythiophene Film Uniformity Using a Cruciform Electrode and Substrate Rotation in Atmospheric Pressure Plasma Polymerization
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Nanomaterials
Volume 12
Issue 1
10.3390/nano12010106
nanomaterials-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Insight into the Properties of Plasmonic Au/TiO2 Activated by O2/Ar Plasma

by
Xiaoqing Deng
1,
Yu Ding
1,
Xiaobing Wang
1,
Xiaojing Jia
1,
Shuo Zhang
2 and
Xiang Li
3,*
1
School of Chemistry and Environmental Engineering, Yangtze University, Jingzhou 434023, China
2
School of Environmental Science and Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, China
3
College of Mechanical Engineering, Yangtze University, Jingzhou 434023, China
*
Author to whom correspondence should be addressed.
Nanomaterials 2022, 12(1), 106; https://doi.org/10.3390/nano12010106
Submission received: 23 November 2021 / Revised: 20 December 2021 / Accepted: 24 December 2021 / Published: 29 December 2021
(This article belongs to the Special Issue Plasma-Enabled Synthesis of Nanostructured Surfaces and Nanoparticles)
Browse Figures
Versions Notes

Abstract

:
The performance of CO oxidation over plasmonic Au/TiO2 photocatalysts is largely determined by the electric discharge characteristics and physicochemical properties of discharge gas. To explore the activation mechanism of Au/TiO2, an O2 and Ar mixture gas as a discharge gas was employed to activate Au/TiO2. The photocatalytic activity in CO oxidation over activated Au/TiO2 was obtained, and the electric discharge characteristics, Au nanoparticle size, surface chemical state, optical property and CO chemisorption were thoroughly characterized. As the O2 content increases from 10% to 50%, the amplitude of the current pulses increases, but the number of pulses and the discharge power decrease. The photocatalytic activity of Au/TiO2 rises rapidly at first and then remains constant at 75% when the O2 content is above 50%. Compared with the discharge gas of 10% and 30% O2/Ar, the sample activated by 50% O2/Ar plasma possesses less metallic Au and more surface oxygen species and carbonate species by X-ray photoelectron spectroscopy, which is consistent with UV-vis diffuse reflectance spectra and CO chemisorption. The CO chemisorption capacities of the activated samples are the same at a long exposure time due to the approximate Au nanoparticle size observed by transmission electron microscopy. An increase in carbonate species generated from the oxygen species on the surface of TiO2 is discovered.

Graphical Abstract

1. Introduction

Au/TiO2, one of the most promising visible-light photocatalysts, can strongly interact with resonant photons in a large faction of the abundant solar flux due to its strong local surface plasmon resonance (LSPR) [1,2,3]. In one of the widely accepted mechanisms, incoming photons and plasmon resonance increase the energy of electrons of Au nanoparticles. These electrons can thus be injected into the conductance band of TiO2 and take part in reactions, leaving a hole behind [4]. This mechanism is analogous to dye sensitization, but noble metals such as Au nanoparticles show more stability and 105 larger charge carrier mobilities than typical dye molecules [5]. Due to its advantages, Au/TiO2 has been widely used as a plasmonic catalyst for water splitting [6,7,8], dye degradation [9,10] and indoor air purification [11,12,13,14] in recent decades. The performance of Au nanoparticles significantly depends on the particle size, which is determined by the conditions of activation. When the size of Au nanoparticles decreases from 3.3 to 2.2 nm, the coordinatively unsaturated sites, such as corners and edges, increase from 23% to 33% [15]. Air calcination, as a traditional method, is usually adopted for activation. This method has a serious drawback in that Au nanoparticles suffer from the risk of sintering and structural collapse caused by high temperatures [16]. More secure and efficient activation methods are urgently necessary.
Recently, cold plasma has been widely considered as a promising activation method [17,18]. The gas temperature of cold plasmas, such as DBD, JET, SDBD, etc., is determined by that of heavy ions and other reactive species, which depends on the gas, such as oxygen, nitrogen atom, NO, etc. The gas temperature is much lower than the electron temperature (1~10 eV) and even close to room temperature [19]. In this case, Au particles on the activated Au/TiO2 catalyst would be highly dispersed rather than aggregated. In addition, cold plasma is rich in high-energy electrons, metastable particles and active radicals. These particles can fully contact the surface of the catalyst to achieve surface modification [20,21,22,23,24]. A suitable discharge atmosphere is one of the most important factors in the plasma activation of Au/TiO2 [25,26,27,28]. The common discharge gases are H2, Ar, O2 and N2. Ar plasma can reduce noble metal nanoparticles and generally presents a greater uniformity and energy efficiency [29,30]. However, excellent discharge properties bring improvement in the efficiency but have an insignificant influence on the activity of catalysts. Ar atmosphere is inferior to other oxidizing atmospheres, such as O2, for the activation of Au nanoparticles. O2 plasma has the ability to enhance the catalytic performance by unique features such as a lower Au nanoparticle size, plenty of surface oxygen, numerous low-coordinated metallic Au and restructuring of the cationic species [27,31,32,33]. O2/Ar plasma is predicted to combine the advantages of Ar plasma and O2 plasma. The investigation of photocatalytic activity on Au/TiO2 activated by plasmas at various O2/Ar ratios would provide insight into the catalytic properties. The relationship between the O2/Ar ratio and physicochemical properties of activated Au/TiO2 also needs to be explored.
In this work, plasmas at various O2/Ar ratios were adopted to activate Au/TiO2. The photocatalytic activity over Au/TiO2 was valued via CO oxidation under visible-light irradiation. The discharge parameters, Au nanoparticle size, optical properties, surface chemical state and CO chemisorption were analyzed. Moreover, the role of O2 in O2/Ar plasma during Au/TiO2 activation is also discussed.

2. Experimental Section

2.1. Preparation of Au/TiO2 Photocatalysts

The preparation of Au/TiO2 photocatalysts was performed by a modified impregnation method, as described in a previous paper [31]. In brief, 1.0 g of P25 (Degussa, Frankfurt, Germany) powder used as the TiO2 support was impregnated with 2.2 mL of 2.43 × 10−2 mol/L HAuCl4 aqueous solution. Then, it was aged for 12 h at room temperature in the dark. Ammonia solution and deionized water were used to wash the powder twice to remove Cl−. After washing and filtering, the cake was dried at 80 °C for 8 h. The as-prepared Au/TiO2 powder was obtained. The actual Au content was approximately 0.90 wt.%, as determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES, Optima 2000DV, New Brunswick, NJ, USA). The coating of Au/TiO2 was obtained for photocatalytic evaluation. The as-prepared Au/TiO2 powder (10 mg) was added to 1 mL of deionized water and sonicated for 15 min. The slurry was coated by the dip-coating method on a 25 mm (L) × 25 mm (W) × 1 mm (T) glass substrate and dried at 80 °C for 0.5 h. The weight of the Au/TiO2 coating was 15 ± 2 mg.

2.2. Plasma Activation and Measurement of Electric Discharge Characteristics

In this paper, plasma was generated by a homemade dielectric barrier discharge at atmospheric pressure to activate Au/TiO2 photocatalysts. The setup scheme is shown in Figure 1. The high-voltage electrode and the ground electrode were covered with aluminum foil and stuck to the upper and lower quartz sheets. The gap between the two quartz sheets was 2 mm. The plasma generator was a sinusoidal AC high-voltage generator with a frequency of 1.8 kHz. The input power was a constant of 5 W under various discharge gases and measured by a wattmeter (D51, 0–75 W; HY, Harbin, China). The discharge gas was a mixture of Ar and O2, each of which was monitored by flow mass control. The total flow rate during the plasma was kept at 100 mL/min. Plasma activation over all samples was conducted for 30 min.
A circuit schematic diagram of electric parameter measurements in DBD plasma is shown in Figure 1. The power meter was accessed on the primary side of the power transformer, and the input power was measured. The discharge voltage was obtained by a high-voltage probe (1000:1), and the discharge current was calculated by measuring the voltage on the sampling resistor, for which the resistor value was 50 Ω. The discharge power was measured by the Lissajous pattern method.

2.3. Photocatalytic Evaluation

The photocatalytic evaluation was carried out under visible light in a continuous flow photocatalytic oxidation reactor. A 300 W X-lamp was employed as the visible-light source, and its wavelength was cut by a 420 nm cutoff filter. The coating sample was placed in the photocatalytic reactor and irradiated through a quartz window (75 mm (L) × 25 mm (W)). The reactant gas was synthetic air (80% N2 + 20% O2) containing approximately 500 ppm CO with a flow rate of 150 mL/min. A COx analyzer (TY-6310, Tianyu Intelligent Control, Wuhan, China) was used to measure CO and CO2 concentrations. Photocatalytic oxidation can be found in detail in a previous study [31]. The reaction time was approximately 40 min when the CO2 concentration reached to a constant. The CO conversion was defined as follows:
X C O ( % ) = C C O i n − C C O o u t C C O i n × 100 %
where C C O i n and C C O o u t represent the concentrations of the CO inlet and outlet gases, respectively.

2.4. Photocatalyst Characterization

The particle size of samples was observed by transmission electron microscopy (TEM, Tecnai G220 S-Twin, FEI, Hillsboro, OR, USA), where 20 mg of Au/TiO2 powder was added into 5 mL of ethanol and dispersed by ultrasound for 15 min. Then, 5 drops of the suspension were dripped on a copper grid with carbon polymer and dried at room temperature for measurement. Chemical binding states and compositions of samples were investigated by X-ray photoelectron spectroscopy (XPS, ESCALAN250, Thermo VG, Boston, MA, USA) using a monochromatized Al Kα (1486.6 eV) X-ray source. All binding energies are referenced to the C 1s peak at 284.6 eV. Diffuse reflectance UV-visible spectra (UV-vis DRS) of samples in a 200–800 nm range were recorded using a spectrophotometer (V–550, JASCO, Tokyo, Japan). Barium sulfate was used as a background reference. The in situ diffuse reflectance infrared Fourier transform (DRIFT) spectra of CO adsorption were recorded by an FT-IR spectrometer (is50, Thermoscientific, Boston, MA, USA) with a MCT detector at a resolution of 4 cm−1. The range of the wavenumber was from 4000 to 1000 cm−1. N2 as a purging gas at a flow rate of 100 mL/min was used to pretreat Au/TiO2 in a DRIFT cell at 80 °C. When the DRIFT cell cooled down to room temperature, the background spectrum was recorded. About 1000 ppm CO/N2 at the same flow rate was switched to the DRIFT cell. Then, spectra of CO adsorption were recorded.

3. Results and Discussion

3.1. Electrical Discharge Characteristics

To gain insight into the plasma activation process, the discharge voltage and discharge current in 10% O2/Ar, 30% O2/Ar and 50% O2/Ar are compared in Figure 2. All the waveforms show a typical filamentary DBD mode in which numerous intense current pulses of micro-discharge appear per half voltage cycle [34,35]. When the O2 content is 10%, the number of current pulses generated by the discharge is large, and the pulse amplitude is small. This result indicates that discharge in 10% O2/Ar plasma is relatively uniform and similar to a typical Ar discharge. As the O2 content increases at a fixed input power, the number of current pulses decreases, and the pulse amplitude increases. The waveforms of the 50% O2/Ar plasma are close to that of O2 discharge. The influence of O2 content on the discharge current can be attributed to the increasing excitation channels, which include dissociation, vibration and rotation of O2 molecules, requiring more energy. The electronegativity is enhanced to form more negative ions with increasing O2 content. The channel contraction and the intensity of micro-discharge channels strengthen [36]. The dependence of discharge power on O2 content is also illustrated in Figure 3. A sharp decrease of discharge power occurs from 2.2 to 1.7 W with the O2 content increasing from 0% to 10%. The power declines very slowly as the O2 content increases from 10% to 50%. The addition of O2 in Ar gas leads to an increase in the intensity of the micro-discharge pulse but a decrease in the number of current pulses, resulting in a decrease in discharge power [37,38]. This means that the efficiency of electrical energy transferred to plasma is weakened with increasing O2 and that the number of activated Au/TiO2 particles decreases in one cycle.

3.2. Photocatalytic Performance

To investigate the effect of the O2/Ar ratio on the visible-light photocatalytic performance, the variations in CO conversion over the samples that were treated with pure Ar, 10% O2/Ar, 30% O2/Ar, 50% O2/Ar, 70% O2/Ar and pure O2 as discharge gases are illustrated in Figure 4. The CO conversion rises rapidly from 40.9% to 63.7% as the O2 content increases from 0% to 10%, and reaches 73.8% at 30% O2/Ar. There is a weak dependence of CO conversion on O2 content as it exceeds 50%. This result proves that O2 plays a vital role in the activation of Au/TiO2. The reason is that Au/TiO2 activated by O2 has more surface oxygen, and the high content of surface oxygen generated in O2 plasma favors superoxide (O2−) formation by accepting hot electrons to promote CO oxidation [25,27,32,33]. However, it is worth noting that the O2 content in O2/Ar plasma is not proportional to the photocatalytic activity. To understand the relationship between physicochemical properties and photocatalytic activity of samples in O2/Ar plasma, various characterizations, such as UV-vis DRS, TEM, XPS and CO chemisorption, were carried out.

3.3. Optical Property

In the visible-light photocatalytic reaction, visible-light absorption of Au/TiO2 is based on the surface plasmon resonance effect of Au0. To investigate the optical properties, UV-vis DRS of Au/TiO2 activated by Ar, 10% O2/Ar, 30% O2/Ar and 50% O2/Ar was measured, as shown in Figure 5. The absorption band of all samples in the visible-light region is centered at 560 nm [39,40], which is attributed to the LSPR absorption bands of Au0. The Au/TiO2 sample activated by Ar plasma has the strongest LSPR absorption peak, inferring the highest content of Au0. As the O2 content in the discharge gas increases, the LSPR absorption peaks become weak and present a slight difference in peak intensity between samples activated by 30% O2/Ar and 50% O2/Ar. This result is consistent with the inset photos shown in Figure 5. The color of the Au/TiO2 sample activated by Ar plasma appears light purple [39,41] and becomes light with increasing O2 content. This is because Au0 nanoparticles absorb green light at approximately 560 nm, and the complementary color is purple. The decreasing Au0 content leads to a lighter purple color. It is suggested that the reduction of cationic Au occurs easily in Ar plasma but is depressed with the addition of O2.

3.4. TEM Observation

It is well-known that the size of Au nanoparticles has a great influence on the photocatalytic activity [42,43,44]. By TEM, the size of Au nanoparticles was observed, as shown in Figure 6. The majority of diameters of Au nanoparticles for samples activated by pure Ar, 10% O2/Ar, 30% O2/Ar and 50% O2/Ar plasmas are around 2 nm. It indicates that the moderate operation of O2/Ar cold plasma inhibits the aggregation of Au nanoparticles and that the O2 content is independent of the size of the Au nanoparticles. Meanwhile, the size distribution of Au nanoparticles slightly decreases as the O2 content rises. This is because the negative charges in the O2/Ar plasma sheath could establish a Coulomb field over the surface of Au nanoparticles to remain highly dispersed.

3.5. Surface Chemical State Analysis

The high-resolution XPS measurements for three samples were characterized to analyze their surface chemical state. XPS spectra of Au 4f, O 1s and C 1s are shown in Figure 7, and the corresponding results of the samples are summarized in Table 1. The chemical valences of Au, surface oxygen and carbonate species were the focus. After fitting analysis, as shown in Figure 7, the XPS spectra of Au 4f can be deconvoluted into Au0 at ~83.1 eV and Au+ at ~84.6 eV [27]. As shown in Table 1, the metallic Au content of the samples decreases from 68.0% to 60.2% with increasing O2 contents, while the cationic Au content rises, demonstrating that the addition of O2 suppresses the reduction of cationic Au. This result is consistent with the intensity sequence of the LSPR peak in UV-vis DRS (Figure 5). The amount of surface oxygen species has a great influence on the photocatalytic activity of CO oxidation. The XPS spectra of O 1s shown in Figure 7b are fitted with three peaks at ~529.5, ~531.6 and ~533.1 eV [45,46], corresponding to the crystal lattice oxygen of TiO2, surface oxygen and adsorbed H2O or carboxyl groups [47,48], respectively. The content of surface oxygen species increases obviously owing to the change in the oxidative atmosphere listed in Table 1. When the O2 content exceeds 30%, the content of surface oxygen slightly increases. The intensity of the peak at ~533.1 eV attributed to C-O species followed a strong dependence on O2 content. In the C 1s spectra, the peaks at ~285.8 and ~288.5 eV are assigned to C-O and C=O [49,50], which also increase with the O2 content, suggesting that adsorbed carboxyl groups were possible on the surface at a higher O2 content.

3.6. CO Chemisorption

With respect to surface species identification, the chemisorption behavior of the CO reactant on the three samples was determined. The evolution of DRIFT spectra of CO adsorbed on Au/TiO2 at room temperature is shown in Figure 8. At the initial time (2 min), all samples show two bonds: one is attributed to CO adsorbed on Au0 at 2108 cm−1 [51,52], and the other is the band near 2160 cm−1 [53,54] attributed to CO adsorbed on Au+. The band of the sample activated by 50% O2/Ar plasma attributed to CO adsorbed on Au0 is highest among the samples. This means that CO chemisorption immediately occurs on the Au nanoparticles where surface oxygen species are abundant. This is because samples with a large number of surface oxygen species provide more electron-deficient metallic gold sites for CO chemisorption [26,55]. At a long exposure time (7 min), only the band attributed to CO adsorbed on Au0 can be found. The band of CO adsorbed on Au+ disappeared along with the significant intensification of CO adsorbed on Au0, indicating that the reduction of cationic Au to metallic Au quickly occurs in the CO reaction. In addition, the heights of the bands of CO adsorbed on Au0 for the samples are the same, inferring that the number of adsorption sites on the samples is approximate, which agrees with the result of Au nanoparticle size in the TEM images. In Figure 8c, the carbonate species whose bands are near 1420 and 1570 cm−1 [56,57] increase with the O2 content, indicating that surface oxygen species on catalysts react with adsorbed CO to generate CO2 escaped from the surface, or that some carbonate species remain during the CO chemisorption process. It can be speculated that the sites of surface oxygen species adsorbed on Au/TiO2 should be different.
In summary, the addition of O2 in Ar gas would destroy the homogenous discharge, and negative charges in the O2/Ar plasma sheath could establish a Coulomb field on the surface of Au nanoparticles to prevent aggregation. The average diameter of Au nanoparticles is approximately 2 nm, as observed in TEM images (Figure 4), and Au/TiO2 activated by plasmas at various O2/Ar ratios presents approximate amounts of CO chemisorption. During plasma activation, O2/Ar plasma prevents cationic Au from reduction and generates more active surface oxygen species on catalysts, as measured by XPS (Figure 7). The active surface oxygen can be reduced into superoxide by hot electrons to participate in CO oxidation, which follows a Langmuir–Hinshelwood mechanism. This means that a catalyst that possesses a large amount of active surface oxygen is sure to have a high activity at the same CO adsorption capacity. The amount of surface oxygen species increases with the O2 content, but CO conversion remains at 75% as the O2 content exceeds 50%. Combining the C 1s spectra in XPS and CO chemisorption over the samples, it can be deduced that there are two sites of active surface oxygen. One is around the interface between Au NPs and TiO2 support, and the other is on the surface of TiO2. The interaction between micro-discharges and Au/TiO2 increases as the O2 content increases. That is, surface oxygen on TiO2 is generated and remains stable. The oxygen species around the interface between Au NPs and TiO2 support engage in CO oxidation to promote the performance. The oxygen species on the TiO2 support form carbonate species, which are irrelevant to photocatalytic activity. As a result, as the O2 content increases, CO conversion rises rapidly and then slightly.

4. Conclusions

The effect of O2 content in O2/Ar plasma on the activation of Au/TiO2 was studied. The number of current pulses decreased, and the pulse amplitude increased with the O2 content. However, discharge power dropped quickly. CO conversion over Au/TiO2 rose rapidly at first and then remained constant once the O2 content reached 50%. Compared with the discharge gas of 10% and 30% O2/Ar, the sample activated by 50% O2/Ar plasma possessed less metallic Au and more surface oxygen species and carbonate species. The CO chemisorption capacities of samples activated by 10%, 30% and 50% O2/Ar plasmas were almost the same at a long exposure time due to the approximate Au nanoparticle size shown in TEM. The content of surface oxygen species slightly increased when the O2 content was over 50%. Carbonate species were generated from the oxygen species on the surface of TiO2 according to the analysis of XPS and CO chemisorption.

Author Contributions

Conceptualization, X.D. and X.L.; formal analysis, X.W.; investigation, X.J.; data curation, Y.D.; writing—original draft preparation, S.Z.; writing—review and editing, Y.D.; visualization, X.D.; supervision, X.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research is funded by the National Natural Science Foundation of China (21808016), the Open Project Program of State Key Laboratory of Petroleum Pollution Control (Grant No. PPC2020010) and the Science and Technology Research Project of the Education Department of Hubei Province (B2021053).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Linic, S.; Christopher, P.; Ingram, D.B. Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy. Nat. Mater. 2011, 10, 911–921. [Google Scholar] [CrossRef] [PubMed]
  2. Willets, K.A.; Van Duyne, R.P. Localized Surface Plasmon Resonance Spectroscopy and Sensing. Annu. Rev. Phys. Chem. 2007, 58, 267–297. [Google Scholar] [CrossRef] [Green Version]
  3. Zhu, S.; Liang, S.; Gu, Q.; Xie, L.; Wang, J.; Ding, Z.; Liu, P. Effect of Au supported TiO2 with dominant exposed {001} facets on the visible-light photocatalytic activity. Appl. Catal. B-Environ. 2012, 119–120, 146–155. [Google Scholar] [CrossRef]
  4. Tian, Y.; Tatsuma, T. Mechanisms and Applications of Plasmon-Induced Charge Separation at TiO2 Films Loaded with Gold Nanoparticles. J. Am. Chem. Soc. 2005, 127, 7632–7637. [Google Scholar] [CrossRef]
  5. Jain, P.K.; Lee, K.S.; El-Sayed, I.H.; El-Sayed, M.A. Calculated Absorption and Scattering Properties of Gold Nanoparticles of Different Size, Shape, and Composition: Applications in Biological Imaging and Biomedicine. J. Phys. Chem. B 2006, 110, 7238–7248. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  6. Zhang, X.; Liu, Y.; Lee, S.-T.; Yang, S.; Kang, Z. Coupling surface plasmon resonance of gold nanoparticles with slow-photon-effect of TiO2 photonic crystals for synergistically enhanced photoelectrochemical water splitting. Energy Environ. Sci. 2014, 7, 1409–1419. [Google Scholar] [CrossRef]
  7. Liu, Z.; Hou, W.; Pavaskar, P.; Aykol, M.; Cronin, S.B. Plasmon Resonant Enhancement of Photocatalytic Water Splitting Under Visible Illumination. Nano Lett. 2011, 11, 1111–1116. [Google Scholar] [CrossRef]
  8. Wang, X.; Long, R.; Liu, D.; Yang, D.; Wang, C.; Xiong, Y. Enhanced full-spectrum water splitting by confining plasmonic Au nanoparticles in N-doped TiO2 bowl nanoarrays. Nano Energy 2016, 24, 87–93. [Google Scholar] [CrossRef]
  9. Naldoni, A.; Riboni, F.; Marelli, M.; Bossola, F.; Ulisse, G.; Di Carlo, A.; Píš, I.; Nappini, S.; Malvestuto, M.; Dozzi, M.V.; et al. Influence of TiO2electronic structure and strong metal–support interaction on plasmonic Au photocatalytic oxidations. Catal. Sci. Technol. 2016, 6, 3220–3229. [Google Scholar] [CrossRef]
  10. Paramasivam, I.; Macak, J.; Schmuki, P. Photocatalytic activity of TiO2 nanotube layers loaded with Ag and Au nanoparticles. Electrochem. Commun. 2008, 10, 71–75. [Google Scholar] [CrossRef]
  11. Corti, C.W.; Holliday, R.J.; Thompson, D.T. Commercial aspects of gold catalysis. Appl. Catal. A-Gen. 2005, 291, 253–261. [Google Scholar] [CrossRef]
  12. Li, W.; Comotti, M.; Schüth, F. Highly reproducible syntheses of active Au/TiO2 catalysts for CO oxidation by deposition–precipitation or impregnation. J. Catal. 2006, 237, 190–196. [Google Scholar] [CrossRef]
  13. Chen, X.; Zhu, H.; Zhao, J.; Zheng, Z.; Gao, X. Visible-Light-Driven Oxidation of Organic Contaminants in Air with Gold Nanoparticle Catalysts on Oxide Supports. Angew. Chem. Int. Ed. 2008, 47, 5353–5356. [Google Scholar] [CrossRef] [PubMed]
  14. Liu, J.; Si, R.; Zheng, H.; Geng, Q.; Dai, W.; Chen, X.; Fu, X. The promoted oxidation of CO induced by the visible-light response of Au nanoparticles over Au/TiO2. Catal. Commun. 2012, 26, 136–139. [Google Scholar] [CrossRef]
  15. Haruta, M. Chance and Necessity: My Encounter with Gold Catalysts. Angew. Chem. Int. Ed. 2014, 53, 52–56. [Google Scholar] [CrossRef]
  16. Tsukamoto, D.; Shiraishi, Y.; Sugano, Y.; Ichikawa, S.; Tanaka, S.; Hirai, T. Gold Nanoparticles Located at the Interface of Anatase/Rutile TiO2 Particles as Active Plasmonic Photocatalysts for Aerobic Oxidation. J. Am. Chem. Soc. 2012, 134, 6309–6315. [Google Scholar] [CrossRef] [PubMed]
  17. Di, L.; Zhang, J.; Zhang, X. A review on the recent progress, challenges, and perspectives of atmospheric-pressure cold plasma for preparation of supported metal catalysts. Plasma Process. Polym. 2018, 15, 1700234. [Google Scholar] [CrossRef]
  18. Li, J.; Ma, C.; Zhu, S.; Yu, F.; Dai, B.; Yang, D. A Review of Recent Advances of Dielectric Barrier Discharge Plasma in Catalysis. Nanomaterials 2019, 9, 1428. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  19. Lu, X.; Laroussi, M.; Puech, V. On atmospheric-pressure non-equilibrium plasma jets and plasma bullets. Plasma Sources Sci. Technol. 2012, 21, 034005. [Google Scholar] [CrossRef]
  20. Xu, L.; Jiang, Q.; Xiao, Z.; Li, X.; Huo, J.; Wang, S.; Dai, L. Plasma-Engraved Co3O4 Nanosheets with Oxygen Vacancies and High Surface Area for the Oxygen Evolution Reaction. Angew. Chem. Int. Ed. 2016, 55, 5277–5281. [Google Scholar] [CrossRef]
  21. Li, Y.; Wang, W.; Wang, F.; Di, L.; Yang, S.; Zhu, S.; Yao, Y.; Ma, C.; Dai, B.; Yu, F. Enhanced Photocatalytic Degradation of Organic Dyes via Defect-Rich TiO2 Prepared by Dielectric Barrier Discharge Plasma. Nanomaterials 2019, 9, 720. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  22. Zhao, Q.; Bu, D.; Li, Z.; Zhang, X.; Di, L. Cold Plasma Preparation of Pd/Graphene Catalyst for Reduction of p-Nitrophenol. Nanomaterials 2021, 11, 1341. [Google Scholar] [CrossRef] [PubMed]
  23. Sharma, R.; Rimmer, R.; Gunamgari, J.; Shekhawat, R.; Davis, B.; Mazumder, M.; Lindquist, D. Plasma-Assisted Activation of Supported Au and Pd Catalysts for CO Oxidation. IEEE Trans. Ind. Appl. 2005, 41, 1373–1376. [Google Scholar] [CrossRef]
  24. Di, L.; Zhan, Z.; Zhang, X.; Qi, B.; Xu, W.; Lanbo, D.; Zhibin, Z.; Xiuling, Z.; Bin, Q.; Weijie, X. Atmospheric-Pressure DBD Cold Plasma for Preparation of High Active Au/P25 Catalysts for Low-Temperature CO Oxidation. Plasma Sci. Technol. 2016, 18, 544–548. [Google Scholar] [CrossRef] [Green Version]
  25. Zhang, J.; Di, L.; Yu, F.; Duan, D.; Zhang, X. Atmospheric-Pressure Cold Plasma Activating Au/P25 for CO Oxidation: Effect of Working Gas. Nanomaterials 2018, 8, 742. [Google Scholar] [CrossRef] [Green Version]
  26. Liu, X.; Mou, C.-Y.; Lee, S.; Li, Y.; Secrest, J.; Jang, B.W.-L. Room temperature O2 plasma treatment of SiO2 supported Au catalysts for selective hydrogenation of acetylene in the presence of large excess of ethylene. J. Catal. 2012, 285, 152–159. [Google Scholar] [CrossRef]
  27. Zhang, S.; Li, X.-S.; Zhu, B.; Liu, J.-L.; Zhu, X.; Zhu, A.-M.; Jang, B.W.-L. Atmospheric-pressure O2 plasma treatment of Au/TiO2 catalysts for CO oxidation. Catal. Today 2015, 256, 142–147. [Google Scholar] [CrossRef]
  28. Sun, Z.-G.; Li, X.-S.; Liu, J.-L.; Li, Y.-C.; Zhu, B.; Zhu, A.-M. A promising visible-light photocatalyst: H2 plasma-activated amorphous-TiO2-supported Au nanoparticles. J. Catal. 2019, 375, 380–388. [Google Scholar] [CrossRef]
  29. Wang, Z.-J.; Xie, Y.; Liu, C.-J. Synthesis and Characterization of Noble Metal (Pd, Pt, Au, Ag) Nanostructured Materials Confined in the Channels of Mesoporous SBA-15. J. Phys. Chem. C 2008, 112, 19818–19824. [Google Scholar] [CrossRef]
  30. Liu, C.-J.; Zhao, Y.; Li, Y.; Zhang, D.-S.; Chang, Z.; Bu, X.-H. Perspectives on Electron-Assisted Reduction for Preparation of Highly Dispersed Noble Metal Catalysts. ACS Sustain. Chem. Eng. 2014, 2, 3–13. [Google Scholar] [CrossRef]
  31. Deng, X.-Q.; Zhu, B.; Li, X.-S.; Liu, J.-L.; Zhu, X.; Zhu, A.-M. Visible-light photocatalytic oxidation of CO over plasmonic Au/TiO2: Unusual features of oxygen plasma activation. Appl. Catal. B-Environ. 2016, 188, 48–55. [Google Scholar] [CrossRef]
  32. Deng, X.-Q.; Liu, J.-L.; Li, X.-S.; Zhu, B.; Zhu, X.; Zhu, A.-M. Kinetic study on visible-light photocatalytic removal of formaldehyde from air over plasmonic Au/TiO2. Catal. Today 2017, 281, 630–635. [Google Scholar] [CrossRef]
  33. Zhu, B.; Zhang, L.-Y.; Liu, J.-L.; Zhang, X.-M.; Li, X.-S.; Zhu, A.-M. TiO2-supported Au-Ag plasmonic nanocatalysts achieved by plasma restructuring and activation. J. Hazard. Mater. 2021, 402, 123508. [Google Scholar] [CrossRef]
  34. Kogelschatz, U. Filamentary, patterned, and diffuse barrier discharges. IEEE Trans. Plasma Sci. 2002, 30, 1400–1408. [Google Scholar] [CrossRef]
  35. Rahel, J.; Sherman, D.M. The transition from a filamentary dielectric barrier discharge to a diffuse barrier discharge in air at atmospheric pressure. J. Phys. D Appl. Phys. 2005, 38, 547–554. [Google Scholar] [CrossRef]
  36. Zhu, B.; Li, X.-S.; Liu, J.-L.; Liu, J.-B.; Zhu, X.; Zhu, A.-M. In-situ regeneration of Au nanocatalysts by atmospheric-pressure air plasma: Significant contribution of water vapor. Appl. Catal. B-Environ. 2015, 179, 69–77. [Google Scholar] [CrossRef]
  37. Masoud, N.; Martus, K.; Figus, M.; Becker, K. Rotational and Vibrational Temperature Measurements in a High-Pressure Cylindrical Dielectric Barrier Discharge (C-DBD). Contrib. Plasma Phys. 2005, 45, 32–39. [Google Scholar] [CrossRef]
  38. Zhang, X.; Cui, Z.; Li, Y.; Xiao, H.; Li, Y.; Tang, J. Study on Degradation of SF6 in the Presence of H2O and O2 Using Dielectric Barrier Discharge. IEEE Access 2018, 6, 72748–72756. [Google Scholar] [CrossRef]
  39. Orendorff, C.J.; Sau, T.K.; Murphy, C.J. Shape-Dependent Plasmon-Resonant Gold Nanoparticles. Small 2006, 2, 636–639. [Google Scholar] [CrossRef]
  40. Xia, Y.; Xiong, Y.; Lim, B.; Skrabalak, S.E. Shape-Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics? Angew. Chem. Int. Ed. 2009, 48, 1. [Google Scholar] [CrossRef]
  41. Zanella, R.; Giorgio, S.; Shin, C.H.; Henry, C.R.; Louis, C. Characterization and reactivity in CO oxidation of gold nanoparticles supported on TiO2 prepared by deposition-precipitation with NaOH and urea. J. Catal. 2004, 222, 357–367. [Google Scholar] [CrossRef]
  42. Zanella, R.; Delannoy, L.; Louis, C. Mechanism of deposition of gold precursors onto TiO2 during the preparation by cation adsorption and deposition–precipitation with NaOH and urea. Appl. Catal. A-Gen. 2005, 291, 62–72. [Google Scholar] [CrossRef]
  43. Zanella, R.; Louis, C. Influence of the conditions of thermal treatments and of storage on the size of the gold particles in Au/TiO2 samples. Catal. Today 2005, 107–108, 768–777. [Google Scholar] [CrossRef]
  44. Boccuzzi, F.; Chiorino, A.; Manzolia, M.; Lub, P.; Akitab, T.; Ichikawab, S.; Harutab, M. Au/TiO2 Nanosized Samples: A Catalytic, TEM, and FTIR Study of the Effect of Calcination Temperature on the CO Oxidation. J. Catal. 2001, 202, 256–267. [Google Scholar] [CrossRef]
  45. Pouilleau, J.; Devilliers, D.; Groult, H.; Marcus, P. Surface study of a titanium-based ceramic electrode material by X-ray photoelectron spectroscopy. J. Mater. Sci. 1997, 32, 5645–5651. [Google Scholar] [CrossRef]
  46. Biener, J.; Farfan-Arribas, E.; Biener, M.; Friend, C.M.; Madix, R.J. Synthesis of TiO2 nanoparticles on the Au(111) surface. J. Chem. Phys. 2005, 123, 094705. [Google Scholar] [CrossRef] [Green Version]
  47. Aguilar-Bolados, H.; Yazdani-Pedram, M.; Quinteros-Jara, E.; Cuenca-Bracamonte, Q.; Quijada, R.; Carretero-González, J.; Avilés, F.; Lopez-Manchado, M.A.; Verdejo, R. Synthesis of sustainable, lightweight and electrically conductive polymer brushes grafted multi-layer graphene oxide. Polym. Test. 2021, 93, 106986. [Google Scholar] [CrossRef]
  48. Yu, J.; Zhao, X.; Zhao, Q. Effect of surface structure on photocatalytic activity of TiO2 thin films prepared by sol-gel method. Thin Solid Film. 2000, 379, 7–14. [Google Scholar] [CrossRef]
  49. Górska, P.; Zaleska, A.; Kowalska, E.; Klimczuk, T.; Sobczak, J.W.; Skwarek, E.; Janusz, W.; Hupka, J. TiO2 photoactivity in vis and UV light: The influence of calcination temperature and surface properties. Appl. Catal. B-Environ. 2008, 84, 440–447. [Google Scholar] [CrossRef]
  50. Dementjev, A.; de Graaf, A.; van de Sanden, M.; Maslakov, K.; Naumkin, A.; Serov, A. X-Ray photoelectron spectroscopy reference data for identification of the C3N4 phase in carbon–nitrogen films. Diam. Relat. Mater. 2000, 9, 1904–1907. [Google Scholar] [CrossRef]
  51. Fierro-Gonzalez, J.; Gates, B.C. Evidence of active species in CO oxidation catalyzed by highly dispersed supported gold. Catal. Today 2007, 122, 201–210. [Google Scholar] [CrossRef]
  52. Bollinger, M.A.; Vannice, M.A. A kinetic and DRIFTS study of low-temperature carbon monoxide oxidation over Au—TiO2 catalysts. Appl. Catal. B-Environ. 1996, 8, 417–443. [Google Scholar] [CrossRef]
  53. Boccuzzi, F.; Chiorino, A. FTIR Study of CO Oxidation on Au/TiO2 at 90 K and Room Temperature. An Insight into the Nature of the Reaction Centers. J. Phys. Chem. B 2000, 104, 5414–5416. [Google Scholar] [CrossRef]
  54. Molina, L.M.; Rasmussen, M.D.; Hammer, B. Adsorption of O2 and oxidation of CO at Au nanoparticles supported by TiO2(110). J. Chem. Phys. 2004, 120, 7673–7680. [Google Scholar] [CrossRef]
  55. Boronat, M.; Concepción, P.; Corma, A. Unravelling the Nature of Gold Surface Sites by Combining IR Spectroscopy and DFT Calculations. Implications in Catalysis. J. Phys. Chem. C 2009, 113, 16772–16784. [Google Scholar] [CrossRef]
  56. Gaur, S.; Wu, H.; Stanley, G.G.; More, K.; Kumar, C.S.; Spivey, J.J. CO oxidation studies over cluster-derived Au/TiO2 and AUROlite™ Au/TiO2 catalysts using DRIFTS. Catal. Today 2013, 208, 72–81. [Google Scholar] [CrossRef]
  57. Hao, Y.; Mihaylov, M.; Ivanova, E.; Hadjiivanov, K.; Knözinger, H.; Gates, B. CO oxidation catalyzed by gold supported on MgO: Spectroscopic identification of carbonate-like species bonded to gold during catalyst deactivation. J. Catal. 2009, 261, 137–149. [Google Scholar] [CrossRef]
Nanomaterials 12 00106 g001 550
Figure 1. Circuit schematic diagram of electrical parameter measurements in plasma. (1) H.V. probe, (2) passive probe, (3) capacitance, (4) resistance, (5) reactor, (6) oscilloscope, (7) AC high-voltage, (8) -COx analyzer.
Figure 1. Circuit schematic diagram of electrical parameter measurements in plasma. (1) H.V. probe, (2) passive probe, (3) capacitance, (4) resistance, (5) reactor, (6) oscilloscope, (7) AC high-voltage, (8) -COx analyzer.
Nanomaterials 12 00106 g001
Nanomaterials 12 00106 g002 550
Figure 2. Waveforms of discharge voltage and discharge current at various O2 contents in O2/Ar discharge gas.
Figure 2. Waveforms of discharge voltage and discharge current at various O2 contents in O2/Ar discharge gas.
Nanomaterials 12 00106 g002
Nanomaterials 12 00106 g003 550
Figure 3. Effect of O2 content in O2/Ar plasmas on discharge power.
Figure 3. Effect of O2 content in O2/Ar plasmas on discharge power.
Nanomaterials 12 00106 g003
Nanomaterials 12 00106 g004 550
Figure 4. Effect of O2 contents in O2/Ar discharge gas on CO conversion.
Figure 4. Effect of O2 contents in O2/Ar discharge gas on CO conversion.
Nanomaterials 12 00106 g004
Nanomaterials 12 00106 g005 550
Figure 5. UV-vis DRS of Au/TiO2 samples activated by Ar plasma, 10% O2/Ar, 30% O2/Ar and 50% O2/Ar plasmas. Inset photos of Au/TiO2 samples activated at various O2 contents.
Figure 5. UV-vis DRS of Au/TiO2 samples activated by Ar plasma, 10% O2/Ar, 30% O2/Ar and 50% O2/Ar plasmas. Inset photos of Au/TiO2 samples activated at various O2 contents.
Nanomaterials 12 00106 g005
Nanomaterials 12 00106 g006 550
Figure 6. TEM images and the associated particle size histograms of the Au/TiO2 samples activated by (a) pure Ar, (b) 10% O2/Ar, (c) 30% O2/Ar and (d) 50% O2/Ar plasmas.
Figure 6. TEM images and the associated particle size histograms of the Au/TiO2 samples activated by (a) pure Ar, (b) 10% O2/Ar, (c) 30% O2/Ar and (d) 50% O2/Ar plasmas.
Nanomaterials 12 00106 g006
Nanomaterials 12 00106 g007 550
Figure 7. XPS spectra of the samples activated by plasmas at various O2 contents in O2/Ar discharge gas: (a) Au 4f, (b) O 1s and (c) C 1s.
Figure 7. XPS spectra of the samples activated by plasmas at various O2 contents in O2/Ar discharge gas: (a) Au 4f, (b) O 1s and (c) C 1s.
Nanomaterials 12 00106 g007
Nanomaterials 12 00106 g008 550
Figure 8. In situ DRIFT spectra of CO adsorption at exposure times of (a) 2 min at the band of 2050~2200 cm−1, (b) 7 min at the band of 2050~2200 cm−1 and (c) 7 min at the band of 1400~1800 cm−1.
Figure 8. In situ DRIFT spectra of CO adsorption at exposure times of (a) 2 min at the band of 2050~2200 cm−1, (b) 7 min at the band of 2050~2200 cm−1 and (c) 7 min at the band of 1400~1800 cm−1.
Nanomaterials 12 00106 g008
Table
Table 1. XPS analysis of the Au/TiO2 samples.
Table 1. XPS analysis of the Au/TiO2 samples.
SamplesProportion (at.%)
Osurf (~531.6 eV)/OAu0/AuAu+/AuC-O/CC-OO/C
Ar14.468.032.032.0
10% O2/Ar16.167.432.68.65.3
30% O2/Ar19.663.336.711.95.9
50% O2/Ar20.060.239.816.37.0
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Deng, X.; Ding, Y.; Wang, X.; Jia, X.; Zhang, S.; Li, X. Insight into the Properties of Plasmonic Au/TiO2 Activated by O2/Ar Plasma. Nanomaterials 2022, 12, 106. https://doi.org/10.3390/nano12010106

AMA Style

Deng X, Ding Y, Wang X, Jia X, Zhang S, Li X. Insight into the Properties of Plasmonic Au/TiO2 Activated by O2/Ar Plasma. Nanomaterials. 2022; 12(1):106. https://doi.org/10.3390/nano12010106

Chicago/Turabian Style

Deng, Xiaoqing, Yu Ding, Xiaobing Wang, Xiaojing Jia, Shuo Zhang, and Xiang Li. 2022. "Insight into the Properties of Plasmonic Au/TiO2 Activated by O2/Ar Plasma" Nanomaterials 12, no. 1: 106. https://doi.org/10.3390/nano12010106

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop