Synthesis of efficient silica supported TiO2/Ag2O heterostructured catalyst with enhanced photocatalytic performance

doi:10.1016/j.apsusc.2017.03.089

Applied Surface Science

Volume 410, 15 July 2017, Pages 454-463

https://doi.org/10.1016/j.apsusc.2017.03.089 Get rights and content

Highlights

•
n-type TiO₂ inside and p-type Ag₂O outside was designed.
•
The p–n junction formation built in an electric field.
•
The p–n junction facilitates the electrons and holes separation.
•
The degradation of dye becomes more effective with Ag₂O/TiO₂ catalyst.

Abstract

We develop the n-type TiO₂ coated on SiO₂ support abbreviated as SiO₂/TiO₂ (ST) followed by deposition of p-type Ag₂O nanoparticles outside for the purpose of photocatalytic degradation of organic pollutants. Different composite catalysts were prepared with changing the amount AgNO₃ (such as 0%, 5%, 10%, 20%, and 30%) and the composites were abbreviated as ST, STA-5, STA-10, STA-20, and STA-30, respectively. The composite catalysts were characterized with different techniques and tested for Rhodamine B (RhB) dye degradation under UV and visible light. Among the composite catalysts, the degradation efficiency of STA-20 was the highest and it degraded about 99% within 40 min under UV light-irradiation. However, the ST, STA-5, STA-10, and STA-30 composite catalysts could degrade about 21%, 47%, 58%, and 75% of the dye, respectively. Furthermore, the STA-5, STA-10, STA-20, and STA-30 composites were also tested and about 39%, 47%, 57%, and 42% of the dye, respectively, was degraded under visible light source. Hence, the formation of p–n junction heterostructure between n-type TiO₂ and p-type Ag₂O could enhance the degradation of RhB in both UV and visible light irradiation. It could be also potentially applicable photocatalyst for environmental remediation.

Graphical abstract

Proposed charge separation mechanism and degradation of dye with photocatalyst under light irradiation.

Introduction

The development of science and technology in the world has led to the growth of urbanization and industrialization it causes the environmental pollutions [1], [2]. Recently, the environmental pollutions caused by organic pollutants are considered as the most serious environmental problems [3], [4]. Particularly, the removal of toxic dyes and other organic compounds from wastewaters effectively, has been the biggest challenge for researchers [5]. For this reason, the growing concerns about solving environmental problems with a green and sustainable technology, such as cleaning of wastewater and removal of organic pollutants with photocatalytic technologies have attracted much attention to researchers [6], [7], [8], [9]. Hence, designing of promising semiconductor photocatalyst materials that can be used to purify water and environmental remediation are significantly important in recent year [10], [11], [12].

Semiconductor materials with suitable band gap such as TiO₂, ZrO₂, ZnO, and ZnS can be used as photocatalysts to degrade organic pollutants under light sources [13], [14], [15], [16], [17]. Because of its high chemical stability, low cost, photosensitivity, and nontoxic nature, TiO₂ is one of the most studied and potentially used photocatalyst semiconductors in recent years [18], [19], [20], [21]. However, TiO₂ alone is not effective and has limited practical photocatalytic application because of its wider band gap, low solar energy conversion efficiency, and low adsorption ability [22], [23]. The recovery process of TiO₂ from the aqueous reaction media is also difficult and limits the industrial applications because the photocatalytic reaction is mostly performed in an aqueous media. Hence, materials that can be used as carriers/support for TiO₂ to separate it easily from an aqueous environment are important and silica was considered to be one of the best supports because of its physical and chemical stability [23]. The SiO₂ particles also used as a substrate to absorb organic pollutants and help TiO₂ to make contact with active site of the dye [24].

Nowadays, the engineering of heterogeneous semiconductor based photocatalysis has been the main research focus, and it is also considered as an efficient tool for solar water splitting and degrading organic pollutants [25], [26]. The photocatalytic activities of semiconductor materials towards degradations of organic pollutants become more efficient when the electron and hole are separated well. On the other hand, lowering the recombination rates of electrons and holes is the basic criteria to improve the photocatalytic activities of the catalysts [27], [28], [29]. The combination of semiconductors with different band gap energy to form heterojunction also improves the physico-chemical properties and the charge separation efficiency [30]. The p-type and n-type semiconductors combination together results in the generation of internal electric field [31], [32], [33]. Particularly metal oxide semiconductor materials such as Cu₂O, Ag₂O, ZnO, and NiO are significantly used together with TiO₂ for the removal of organic pollutants [29], [34], [35], [36].

Among metal oxide semiconductors, Ag₂O is promising photocatalyst because of its suitable band gap energy position (1.2 eV), easy to prepare, and highly efficient material towards removal of organic pollutants [37], [38], [39]. In heterojunction formation between p-type Ag₂O and n-typeTiO₂, the Ag₂O nanoparticles are used to trap electron to increase the electron and hole separation efficiency generated under ultraviolet light and widen the range of photo-response to the visible region [40]. Due to this reason, the Ag₂O based composite catalysts are considered as an alternative and efficient photocatalyst materials to solve environmental related issues [41], [42].

In this work, we design the synthesis of p–n based heterostructured composite catalyst, which is inherently facile method, from n-type TiO₂ and p-type Ag₂O semiconductors. The formation of p–n heterojunctions facilitates the electron–hole separation because it can build an electric field within the photocatalytic system. Separation of electrons and hole during reaction improve the photocatalytic activity of the catalyst. The photogenerated holes efficiently oxidize organic pollutants into water and CO₂. The photogenerated electrons are trapped by Ag₂O nanoparticles, and more holes will be freely available to degrade the pollutants. Moreover, the amount of Ag₂O loading is also important for catalytic activities. Therefore, the optimum amount of Ag₂O loaded on ST composite catalysts is demonstrated. RhB dye is used as a model organic pollutant to test our composite catalyst.

Section snippets

Chemicals

The chemicals and reagents were analytical-grade and used without further purification.

Preparation of SiO₂ sphere

The preparation of SiO₂ spherical particles was done according to our previous work [43]. Briefly, 1.2 g of cetyltrimethylammonium bromide (CTAB) was added in to absolute ethanol (160 mL) and DI water (240 mL) mixture and ultrasonicated for 1 min. In the reaction mixture, 3.2 mL ammonium hydroxide was added followed by continuous stirring for 30 min. Then, 4 mL of TEOS (tetraethyl orthosilicate) was also added and

Characterizations of the composite catalyst

XRD patterns of the powder samples for SiO₂, Ag₂O, ST, STA-5, STA-10, STA-20, and STA-30 were characterized (Fig. 1a). As it is shown from Fig. 1a, the amorphous phase of pure SiO₂ (S) and the XRD patterns of the as-prepared Ag₂O (A) were demonstrated for comparison purpose. The XRD patterns of the cubic Ag₂O phase with the major peaks located at 2θ values of 32.8°, 38.9°, 55.0°, and 65.5° were observed (JCPDS No. 65-6811). Furthermore, XRD pattern of TiO₂ after coated on the surface of

Conclusions

The Ag₂O and TiO₂ heterostructures deposited on SiO₂ support were synthesized with facile method and the formed composite catalysts were characterized by XRD, SEM, HRTEM, and XPS. The STA-20 composite catalyst prepared with 20% Ag precursor showed the highest degradation efficiency and about 99% of RhB dye was degraded within 40 min under UV light-irradiation. The mechanism under UV-light irradiation demonstrates that the Ag₂O semiconductor is used as an electron absorbent and enhances

Acknowledgments

This work was supported by Ministry of Science and Technology of the Republic of China through Grant MOST 104-2221-E- 011-169-MY3 and National Taiwan University of Science and Technology under the Grant 105H451714.

References (58)

M.J. Ahmed et al.
A facile synthesis of Fe₃O₄-charcoal composite for the sorption of a hazardous dye from aquatic environment
J. Environ. Manage.
(2015)
J. Wen et al.
Photocatalysis fundamentals and surface modification of TiO₂ nanomaterials
Chin. J. Catal.
(2015)
R.a. He et al.
Recent advances in visible light Bi-based photocatalysts
Chin. J. Catal.
(2014)
P. Bansal et al.
Comparative study of catalytic activity of ZrO₂ nanoparticles for sonocatalytic and photocatalytic degradation of cationic and anionic dyes
Chem. Eng. J.
(2015)
R. Khan et al.
Facile synthesis of ZnO nanoglobules and its photocatalytic activity in the degradation of methyl orange dye under UV irradiation
Mater. Lett.
(2015)
L. Hu et al.
Hydrothermal synthesis of SnO₂/ZnS nanocomposite as a photocatalyst for degradation of Rhodamine B under simulated and natural sunlight
J. Mol. Catal. A: Chem.
(2016)
M. Mazur et al.
Functional photocatalytically active and scratch resistant antireflective coating based on TiO₂ and SiO₂
Appl. Surf. Sci.
(2016)
Y. Li et al.
Synthesis and characterization of Cu₂O/TiO₂ photocatalysts for H₂ evolution from aqueous solution with different scavengers
Appl. Surf. Sci.
(2015)
D.S. Kim et al.
The hydrothermal synthesis of mesoporous TiO₂ with high crystallinity, thermal stability, large surface area, and enhanced photocatalytic activity
Appl. Catal. A
(2007)
K.P.O. Mahesh et al.
Synthesis of Ni nanoparticles decorated SiO₂/TiO₂ magnetic spheres for enhanced photocatalytic activity towards the degradation of azo dye
Appl. Surf. Sci.
(2015)

J. Low et al.

Surface modification and enhanced photocatalytic CO₂ reduction performance of TiO₂: a review

Appl. Surf. Sci.

(2017)

Cited by (69)

Recent progress on plant extract-mediated biosynthesis of ZnO-based nanocatalysts for environmental remediation: Challenges and future outlooks
2023, Advances in Colloid and Interface Science
The plant extract mediated green synthesis of nanomaterials has attracts enormous interest due to its cost-effectiveness, greener, and environmentally friendly. It is also considered as an alternative and facile method in which the phytochemicals can be used as a natural capping and reducing agents and helped to produce nanomaterials with high surface area, different sizes, and shapes. One of the materials fabricated using green methods is zinc oxide (ZnO) semiconductor due to its enormous applications in different field areas. In this review, an overview of recent progress on green synthesized ZnO-based catalysts and various modification methods for the purpose of enhancing the catalytic activity of ZnO and the corresponding structural-activity and interactions towards the removal of pollutants are highlighted. Particularly, the plant extract mediated ZnO-based photocatalysts application for the removal of pollutants via photocatalytic degradation, reduction reaction, and adsorption mechanism are demonstrated. Besides, the opportunities, challenges, and future outlooks of ZnO-based materials for environmental remediation with green and sustainable methods are also included. We believe that this review is a timely and comprehensive review on the recent progress related to plant extract mediated ZnO-based nanocatalysts synthesis and applications for environmental remediation.
Highly photoactive novel NiS/BiOI nanocomposite photocatalyst towards efficient visible light organic pollutant degradation and carcinogenetic Cr (VI) reduction for environmental remediation
2023, Chemosphere
Heterojunction engineering in catalyst structures is a promising approach for solving the main restriction of the narrow photoabsorption range and quick recombination of photogenerated charge carriers in the photocatalysts. Herein, a simple, eco-friendly, non-toxic, and novel Z-scheme heterojunction of nanoflower-like NiS/BiOI was systematically designed using the low-temperature solvothermal and precipitation methods. The physicochemical and photo-electrochemical properties of the as-synthesized nanomaterials were characterized using XRD, FESEM, FT-IR, XPS, BET, UV–vis, PL, and EIS. NiS/BiOI nanomaterials exhibited a wide photoabsorption range (200–1000 nm), a narrow bandgap energy (1.76 eV), a large surface area (35.82 m² g^-1), and a low charge carrier recombination rate because of the synergistic effects of the NiS and BiOI photocatalysts, which could be the basis for superior photocatalytic efficiency. Particularly, the optimal 40% NiS/BiOI nanocomposite exhibited better stability and efficiency than the pure NiS and BiOI. The maximum degradation efficiency of rhodamine B (RhB) was 99.8% after 200 min, tetracycline (TC) was 96.3% after 140 min, and the photoreduction of Cr(VI) was 92.8% after 180 min rather than the pure NiS and BiOI under visible light irradiation. The constant rate (k) of RhB was approximately 10 and 4, TC was 12 and 4, and Cr(VI) was 10 and 8 times that of pristine NiS and BiOI, respectively. Radical trapping experiments and Tauc plot analysis proposed the design of the plausible Z-scheme reaction mechanism between NiS and BiOI, which has a crucial role in the rate of transportation and separation of electron/hole pairs. This investigation provides a venue for the design of a photoactive NiS-based nanocomposite for environmental remediation.
Preparation and photocatalytic performance of a magnetically recyclable ZnFe<inf>2</inf>O<inf>4</inf>@TiO<inf>2</inf>@Ag<inf>2</inf>O p-n/Z-type tandem heterojunction photocatalyst: Degradation pathway and mechanism
2023, Colloids and Surfaces A: Physicochemical and Engineering Aspects
The high recombination rate of photoelectron-hole pairs and the difficulty separating the catalyst from the solution severely restrict the development of photocatalysis. The construction of heterojunctions and the loading of magnetic carriers are considered to be effective solutions to these two problems. Against this background, a magnetically recoverable ZnFe₂O₄ @TiO₂ @Ag₂O heterojunction composite photocatalyst was prepared. Under the optimum preparation conditions, the degradation rate of rhodamine B (RhB) by the composite catalyst under ultraviolet(UV) light reached 98.4% within 40 min; the kinetic constant k was 0.09449 min⁻¹, which was 39.2, 2.0 and 7.8 times those of ZnFe₂O₄, TiO₂ and Ag₂O alone, respectively, and the removal rate of total organic carbon (TOC) reached 63.2%. In addition, the catalyst also showed good magnetic recovery performance and reusability. A series of characterization and mechanism research results show that the excellent photocatalytic performance is due to the synergistic effect of the Z-type heterojunction and p-n junction, which promotes the separation and transfer efficiency of photogenerated electron-hole pairs. In conclusion, this work provides new insight into the preparation of magnetically recoverable heterojunction photocatalysts and their application in the degradation of organic pollutants.
Probing of silver oxide nanoblades for 4-hydroxybenzoic acid quantification: a tool for food and water safety assessment
2022, Materials Today Chemistry
From various emerging harmful contaminants, 4-hydroxybenzoic acid (HBA) has gained considerable recent attention due to its penetration into certain consumer products. In our research, for the first time, we report the synthesis and utilization of novel-shaped silver oxide nanoblades (Ag₂O NBs) towards direct electrochemical sensing of HBA. The synthesis of Ag₂O NBs was accomplished using a chemical method to produce nanoblades with a thickness of 15–20 nm, high homogeneity (band gap 2 eV), crystallinity, and a cubic unit cell. The electrocatalytic competence of the synthesized Ag₂O NBs was established through their admittance behavior and capability towards oxidation of HBA. The fabricated Ag₂O NBs/Nafion/Au electrode was evaluated electrochemically for its conduction behavior and electrocatalytic activity towards oxidation of 4-hydroxybenzoic acid (HBA) into phenoxonium ion. A cyclic voltammetry (CV) technique was standardized and optimized for the determination of HBA content in authentic samples, and the results were found to be in close agreement with that of spiked samples. The selectivity of the fabricated electrode and standardized technique was also evaluated in the presence of potential interfering species. This fabricated sensor demonstrated a detection limit of 4.58 ppm (linear range: 5–50 ppm) and sensitivity of 83.87 μA cm⁻² ppm⁻¹. Additionally, the practicability of the fabricated sensor was realized through analysis of various types of field samples.
Removal of PFASs from water by carbon-based composite photocatalysis with adsorption and catalytic properties: A review
2022, Science of the Total Environment
Per- and polyfluoroalkyl substances (PFASs) are a class of persistent organic pollutants widely distributed in aquatic environments. The adsorption and photocatalytic methods have been widely used to remove PFASs in water because of their respective advantages. Still, they have apparent defects when used alone. Therefore, the adsorption and photocatalytic technologies are combined through suitable preparation methods, and the excellent properties of the two are used to synergize the treatment of organic pollutants. This strategy of “concentrating” pollutants and then degrading them in a centralized manner plays an essential role in removing trace PFASs. Nevertheless, a review focusing on this kind of adsorption photocatalyst system is lacking. This review will fill this gap and provide a reference for developing a carbon-based composite photocatalyst. Firstly, different carbon-based composite photocatalysts are reviewed in detail, focusing on the differences in various composite materials' excellent adsorption and catalytic properties. Secondly, the factors influencing the removal effect of carbon-based composite photocatalysts are discussed. Thirdly, the removal mechanism of carbon-based composite photocatalysts is summarized in detail. The removal process involves two steps: adsorption and photodegradation. The adsorption process involves multiple cooperative adsorption mechanisms, and photocatalytic degradation includes oxidative and reductive degradation. Fourthly, the comparison of adsorption-photocatalysis with common treatment techniques (including removal rate, range of adaptation, cost, and the possibility of expanding application) is summarized. Finally, the prospects of carbon-based composite photocatalysts for repairing PFASs are given by evaluating the performance of different composites.
Insight into the catalytic performance of silver oxides towards peroxymonosulfate activation for pollutants degradation: Efficiency, mechanism and stability
2022, Colloids and Surfaces A: Physicochemical and Engineering Aspects
Silver-based materials have emerged as excellent catalysts for peroxymonosulfate (PMS) activation in wastewater pollutants degradation. However, the mechanism of pure silver oxides towards PMS activation remains insufficient. In this work, Ag₂O and AgO were selected as typical silver oxides to detect the catalytic performance. AgO/PMS possessed higher activity for p-nitrophenol and other pollutants degradation than Ag₂O/PMS. The stability experiment and structure changes characterized from XRD, FTIR, and XPS, as well as quenching research, demonstrated that SO₄^•− was the main free radical produced from the oxidation of Ag(I) to Ag(II) and reduction of Ag(II) to Ag(I) by PMS; meanwhile, the high valence Ag(II) could directly oxidize the pollutants, which was also contributable to the degradation. Compared with Ag₂O, AgO exhibited better efficiency and recyclability. These results provide key mechanistic insights into silver oxides towards PMS activation.

View all citing articles on Scopus

View full text

Synthesis of efficient silica supported TiO2/Ag2O heterostructured catalyst with enhanced photocatalytic performance

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals

Preparation of SiO2 sphere

Characterizations of the composite catalyst

Conclusions

Acknowledgments

J. Environ. Manage.

Chin. J. Catal.

Chin. J. Catal.

Chem. Eng. J.

Mater. Lett.

J. Mol. Catal. A: Chem.

Appl. Surf. Sci.

Appl. Surf. Sci.

Appl. Catal. A

Appl. Surf. Sci.

Appl. Surf. Sci.

Appl. Surf. Sci.

J. Mol. Catal. A: Chem.

J. Hazard. Mater.

Ceram. Int.

Appl. Surf. Sci.

Appl. Surf. Sci.

J. Alloys Compd.

Chem. Eng. J.

Appl. Surf. Sci.

Appl. Surf. Sci.

Appl. Surf. Sci.

Ceram. Int.

Appl. Surf. Sci.

Appl. Catal. B

Appl. Surf. Sci.

Appl. Surf. Sci.

J. Mol. Catal. A: Chem.

Appl. Surf. Sci.

Synthesis of efficient silica supported TiO₂/Ag₂O heterostructured catalyst with enhanced photocatalytic performance

Preparation of SiO₂ sphere