Elsevier

Chemosphere

Volume 305, October 2022, 135497
Chemosphere

Highly porous seeding-free boron-doped ultrananocrystalline diamond used as high-performance anode for electrochemical removal of carbaryl from water

https://doi.org/10.1016/j.chemosphere.2022.135497Get rights and content

Highlights

  • Easy-to-prepare BDD-based electrode, highly efficient tool to remove recalcitrant pollutants in water.

  • In 30 min, carbaryl was completely removed from a synthetic medium, consuming 4.01 kWh m−3 order−1.

  • In real water - complete CBR degradation within 20–60 min with TOC removal of 52.3–65.5%.

  • Carboxylic acids were detected and nitrogen-based ions were within the established maximum contamination levels.

Abstract

Boron-doped diamond (BDD) electrodes are regarded as the most promising catalytic materials that are highly efficient and suitable for application in advanced electrochemical oxidation processes targeted at the removal of recalcitrant contaminants in different water matrices. Improving the synthesis of these electrodes through the enhancement of their morphology, structure and stability has become the goal of the material scientists. The present work reports the use of an ultranano-diamond electrode with a highly porous structure (B-UNCDWS/TDNT/Ti) for the treatment of water containing carbaryl. The application of the proposed electrode at current density of 75 mA cm−2 led to the complete removal of the pollutant (carbaryl) from the synthetic medium in 30 min of electrolysis with an electric energy per order of 4.01 kWh m−3 order−1. The results obtained from the time-course analysis of the carboxylic acids and nitrogen-based ions present in the solution showed that the concentrations of nitrogen-based ions were within the established maximum levels for human consumption. Under optimal operating conditions, the proposed electrode was successfully employed for the complete removal of carbaryl in real water. Thus, the findings of this study show that the unique, easy-to-prepare BDD-based electrode proposed in this study is a highly efficient tool which has excellent application potential for the removal of recalcitrant pollutants in water.

Introduction

Anodic oxidation (AO) is one of the major electrochemically-driven technologies which have been widely applied for the remediation of recalcitrant organic substances - including dyes, personal care and pharmaceutical products, and pesticides, usually present in water bodies (Sirés and Brillas, 2012; Sirés et al., 2014; Baddouh et al., 2018; Garcia-Segura et al., 2018b; Martínez-Huitle and Panizza, 2018; dos Santos et al., 2021b). AO is considered an environmentally friendly technique as the process does not require the use of chemicals and oxidants are electrogenerated in situ. Several studies have shown that the electrocatalytic properties of the anode material are among the main factors that determine the efficiency of the AO process (Panizza and Cerisola, 2009; Sirés et al., 2014; Moreira et al., 2017; dos Santos et al., 2019, 2021a). In this context, boron-doped diamond (BDD) anode is regarded as the best material for application in AO due to its excellent properties including high stability, inert surface, and large O2 overpotential window (Kapałka et al., 2009). The large O2 overpotential window of BDD anode helps generate a huge amount of oxidant species such as physiosorbed hydroxyl radicals (M(radical dotOH), Eq. (1) which can attack organic pollutants (R) non-selectively, turning them into non-hazardous products or even leading them to complete combustion, as shown in Eq. (2) below (do Vale-Júnior et al., 2019; Brillas, 2021; Karim et al., 2021; Mostafa et al., 2021).M + H2O → M(radical dotOH) + H+ + eaM(radical dotOH) + R → mCO2 + nH2O + xH+ + ye

The properties of BDD can be enhanced considerably by varying the concentration of boron, film thickness, and sp2/sp3 ratio, as well as the electrode morphology and porosity (Baluchová et al., 2019; Mei et al., 2019). As pointed out in the literature, one can promote the contact between the electrolyte and the electrode by increasing the electrochemical surface area through the adjustment of the film porosity from macro to nano-porous depending on both the porosity of the substrate and specific post-growth treatment on the diamond surface. So far, a number of studies reported in the literature have employed the seeding substrate pre-treatment mechanism to boost the diamond growth through the application of the chemical vapor deposition technique (Wei et al., 2009; Szunerits et al., 2015; Yang et al., 2016). This pre-treatment mechanism involves the use of diamond powder to improve diamond growth since diamond is unable to grow naturally on non-diamond substrates. Due to the fast deposition kinetics, this seeding substrate pre-treatment procedure, which boosts the diamond growth, favors the formation of agglomerated structures; on the other hand, the fast deposition kinetics makes it harder to obtain structures with nano or ultranano-porosity which are more suitable and efficient for improving the efficiency of the AO process (May and Mankelevich, 2008; Luong et al., 2009; Macpherson, 2015).

As an alternative to the typical BDD synthesis method, in a previous study (Vernasqui et al., 2022), our research group proposed the use of an innovative boron-doped ultrananocrystalline diamond grown on titanium dioxide nanotube without the seeding substrate pre-treatment procedure (B-UNCDWS/TDNT/Ti). The use of titanium dioxide nanotubes (TDNT) allows spontaneous diamond growth under slower deposition kinetics compared to the seeding process, and this enables one to have higher control of deposition and the ability to produce extremely thin films, in addition to maintaining the porosity of the substrate material. This approach represents a major step forward in the synthesis of BDD and helps explore the unique properties of BDD when it comes to the treatment of recalcitrant pollutants. Thus, this study evaluates the efficiency of the innovative B-UNCDWS/TDNT/Ti electrode when applied for the removal of carbaryl (CBR) pesticide in both synthetic and real media under the AO process. Carbaryl is a broad-spectrum N-methyl carbamate insecticide applied worldwide for the control of pests during the production of crops (cotton, corn, soybean, nut, fruits, and vegetables) and for the protection of lawns, home gardens and other ornamental plants (Koshlukova and Reed, 2014).

CBR ranks second among the insecticides that are commonly detected in surface water (Nair et al., 2022). CBR can dissolve in water, migrate through soil, and find its way into groundwater, contaminating it (Wu et al., 2019). People are mostly exposed to CBR through the intake of food and water or other liquids. Depending on the individual and the dose of CBR ingested into the body, the person may experience a variety of symptoms which range from weakness to reduced heart and lung function. In view of that, it is essential to develop techniques that are capable of removing this type of contaminant from food and water so as to prevent excessive human exposure to this pollutant and the occurrence of severe health problems in humans. To analyze the efficiency and viability of the proposed anode in terms of CBR degradation, different current densities were tested, and the best operating conditions were applied for the analysis of real drinking water with a view to evaluating the potential of the technique in real applications. The presence of different oxidants in the system was evaluated using scavenger compounds. Energetic figures of merit were calculated, and the evolution of intermediates produced during the treatment process was also thoroughly monitored. For comparison purposes, the study also provides comprehensive data related to the physical and electroanalytical characterization of the proposed B-UNCDWS/TDNT/Ti anode.

Section snippets

Chemical reagents

Carbaryl (CBR) pesticide (99% purity, Sigma-Aldrich) was used as a model pollutant. Analytical grade potassium sulfate – acquired from Neon, was used as supporting electrolyte; methanol (MeOH) and tert-butanol (TBH), both acquired from Sigma Aldrich, were used as scavengers; and acetonitrile – obtained from Merck, was used as mobile phase for the conduct of high-performance liquid chromatography (HPLC) analysis. All reagents were used directly without extra purification. Ultrapure water from a

Morphological, physical, and electrochemical characterizations of the B-UNCDWS/TDNT/Ti

Fig. 1a-d shows the remarkable homogeneous morphology of the UNCDWS/TDNT/Ti with different growth planes obtained after chemical vapor deposition on TDNT in different magnifications. As can be observed, the entire surface of the electrode is covered by a thin layer, and one will notice the presence of a diamond film in the pore walls which helps maintain the porosity of the electrode surface. Furthermore, one can see clusters of ballas diamond which are distributed on the sample surface. In the

Conclusions

The present work reported the synthesis of B-UNCDWS/TDNT/Ti electrodes with extremely thin diamond films using an innovative methodology without seeding substrate pre-treatment and their successful application for the treatment of water containing recalcitrant compounds. The material proposed in this study was found to possess suitable electrochemical properties, including highly porous ultranano-structures, improved specific capacitance (274 μF cm−2) and high onset potential for water

Author statement

L. G. Vernasqui: Methodology, Investigation, Writing - original draft. A. J. dos Santos: Investigation, Conceptualization, Methodology, Writing - original draft, Writing - review & editing. G. V. Fortunato: Investigation, Conceptualization, Methodology, Writing - original draft, Writing - review & editing. M. S. Kronka: Investigation, Writing - review & editing. H. L. Barazorda-Ccahuanac: Conceptualization, Writing - original draft. A. S. Fajardo: Conceptualization, Writing - original draft,

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 authors acknowledge the financial support provided by the following Brazilian research funding agencies: Brazilian National Council for Scientific and Technological Development - CNPq (grant #465571/2014-0 and #303943/2021–1), São Paulo Research Foundation - FAPESP (grants #2014/50945–4, #2017/23464–3, #2017/10118–0, #2019/04421–7, #2019/20634–0, #2019/00592–1 and #2021/07615–7) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES – Finance Code 001) in support of this

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