Enhancing electrochemical and photoelectrochemical degradation of organic dyes under visible irradiation with a novel Cu2O/BaHPO4-based photoelectrode

https://doi.org/10.1016/j.jallcom.2023.170822Get rights and content

Highlights

  • The Cu2O/BaHPO4 photoelectrode was successfully synthesized and characterized.

  • The Cu2O/BaHPO4 composite exhibited enhanced electrocatalytic and photo-electrocatalytic activity and stability.

  • HO. and O2-. radicals were confirmed as the predominant reactive species for RhB dye degradation.

  • The mechanism was proposed based on the synergistic effect between Cu2O and BaHPO4.

Abstract

A highly active Cu2O/BaHPO4 photoanode was obtained using a simple two-step electrodeposition technique. The synthesised material was characterised by various methods, including X-ray diffraction (XRD), which revealed the orthorhombic phase of BaHPO4 and the cubic phase of Cu2O, while scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDX) showed the platelet and prism morphology of BaHPO4 and Cu2O, respectively. The optical features of both compounds as well as their band gap energies were also evaluated and calculated using diffuse reflection spectroscopy (DRS). The vibrational properties of the photoanode were studied using Fourier transform infrared (FT-IR). The electrocatalytic activity (EC) of the samples were evaluated using a central composite design for surface response methodology (CCD-RSM) to determine the optimal conditions for Rhodamine B (RhB) degradation. The photoelectrocatalytic performance (PEC) of the Cu2O/BaHPO4 photoanode was about 98% in 5 min of reaction under visible irradiation, which was higher than BaHPO4 and Cu2O alone significating a quick separation of photoexcited carriers thanks to the excellent synergetic properties exhibited by the composite. This finding was corroborated by the results obtained from electrochemical impedance spectroscopy (EIS) and Mott-Schottky (MS) analysis. Various cationic and anionic dyes could be efficiently degraded. In addition, after 8 cycles, a non-significant decrease in the degradation rate was observed confirming the high cyclability of the photoanode. Therefore, Cu2O/BaHPO4 can be considered as a promising candidate for the efficient degradation of organic pollutants.

Introduction

The surge in water pollution in recent years has caused a severe global energy crisis and environmental issues, posing a threat to the survival of humans and many other species [1], [2], [3], [4], [5], [6], [7], [8] Therefore, environmental remediation has been expensively studied with the attention to photoelectrocatalytic degradation. This process is considered as a potential solution to break down organic pollutants that cannot be treated by biological methods due to its eco-friendly, versatile, and safe nature [9], [10]. Photoelectrocatalysis has the potential to lower the recombination of electron-hole charges by applying a bias potential [11].

Among various semiconductors, barium hydrogen phosphate (BaHPO4), an n-type semiconductor, has been identified as a suitable material for treating water pollution [12]. BaHPO4 is commonly used as a host lattice due to its luminescent properties, while its high electrocatalytic and photoelectrocatalytic efficiency is attributed to its valence band (VB) of 2.52 V vs NHE, its conduction band (CB) − 0.97 V vs NHE, and a coordinated band gap of 3.9 eV. However, this semiconductor has the disadvantage of being activated only in the UV range and unstable when applying a high current density [12].

One of the most common methods to improve the properties of a semiconductor is the formation of composite materials by combining it with another semiconductor in order to decrease its band gap. Thus, obtaining a visible light active material [13]. This approach offers opportunities for enhancing optoelectronic properties, engineering band gaps, improving charge transport and separation, achieving synergistic functionality, and increasing material versatility [14], [15], [16]. These advantages contribute to the development of new semiconductor-based devices and technologies with enhanced performance and efficiency [17], [18].

The adopted approach for enhancing the optical and catalytic properties of the BaHPO4 catalyst involves modifying it through the incorporation of a material with a narrower bandgap energy. This material can be activated by visible light, resulting in the generation of electrons that transfer to the BaHPO4 catalyst, while leaving positively charged holes. This charge separation phenomenon enhances the performance of the catalyst and contributes to its improved optical and catalytic properties.

Cu2O semiconductor is a plentiful and non-toxic material with a small band-gap of 2.1 eV [19], [20], [21], [22], [23], [24], [25]. It also has a superior absorption coefficient [26], and can be easily produced using low-cost techniques, particularly electrodeposition [27], [28], [29], [30], [31], [32].

In this context, the cuprous oxide Cu2O was electrochemically deposited on BaHPO4, which is itself deposited on the FTO substrate and utilized as a dynamic photoanode for the oxidation of a model dye Rhodamine B (RhB).

To improve the degradation of RhB, a statistical technique called response surface methodology (RSM) was adopted to determine the optimal values for various parameters considered affecting the most the degradation efficiency. Through a deep analysis of the relationship between different independent variables, RSM allows to identify the most effective and dependable conditions for achieving greater RhB degradation.

The novelty of this research lies in creating a novel electrode by combining barium hydrogen phosphate, which is recognized for its potential to degrade organic pollutants, and cuprous oxide, possessing a bandgap energy in the visible area. This new electrode was employed to assess the synergistic impact of these two materials on the degradation of Rhodamine B and other dyes.

Section snippets

Chemicals

All the chemicals used in the experiment were of analytical grade and used without any additional purification. Barium nitrate (Ba(NO3)2, 99%, Fluka), ammonium dihydrogen phosphate ((NH4)H2PO4, 100%, Fluka), tartaric acid (C4H6O6, 99.5%, Sigma–Aldrich), copper (II) sulphate 5-hydrate (CuSO4.5H2O, 99.5–102.0%, Sigma–Aldrich), L-ascorbic acid (C6H8O6, ≥ 99%, Sigma–Aldrich), ethylenediaminetetraacetic acid disodium EDTA-2Na (C10H14N2Na2O8, ≥ 99–101%, Sigma–Aldrich), isopropanol IPA (C3H8O, ≥99.6,

Cyclic voltammetry and Chronopotentiometry studies of BaHPO4

The cyclic voltammetry was made in order to study the electrochemical stability window for the electrodeposited BaHPO4. The potential was scanned between 0 and − 2 V vs SCE, with a speed of 20 mV.s−1, where the electrolytic solution contains the following ions NO3-, Ba2+, NH4-, H2PO4-, H3O+ and HO-.

The voltammogram in Fig. 1(a) shows an increase in the cathodic current while decreasing the potential from − 0.5 to − 1.4 V vs SCE. This cathodic peak is attributed to the reduction of nitrate ions

Conclusion

In brief, we have successfully synthesized a copper oxide and barium hydrogen phosphate-based photoanode that enhances the photoelectrocatalytic efficiency of both compounds. Through CCD-RSM analysis, we determined the optimal conditions for degrading Rhodamine B, a model dye. Under the following conditions ([NaCl]=0.26 M, [RhB]=9.80 ppm, I=8.40 mA. cm2 and pH=6.40), the electrode exhibited maximum electrocatalytic performance during a 15 min reaction time. By applying visible irradiation

CRediT authorship contribution statement

Ayoub Ahdour: Experimental analysis, original manuscript draft preparation and reviewing the manuscript. Elhassan Amaterz: Methodology, investigation. Aziz Taoufyq: Validation, editing, investigation, and supervision. Latifa Aneflous: Validation, editing, investigation, and supervision. Bahcine Bakiz: Validation, revision. Khadija Abouabassi: Data curation. Ahmed Ihlal: Validation, revision. Abdeljalil Benlhachemi: Conceptualisation, validation, revision, editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The research was conducted at the Laboratory of Materials and Environment (LME) located at the Faculty of Sciences in Agadir, Ibn Zohr University. Financial support for this work was provided by the PPR project under the grant number PPR/2015/32, which was funded by the Moroccan National Center for Scientific and Technical Research (CNRST).

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