Design of highly efficient porous carbon foam cathode for electro-Fenton degradation of antimicrobial sulfanilamide

Dedicated to the memory of Prof. Maria Flytzani-Stephanopoulos (1950 - 2019).
https://doi.org/10.1016/j.apcatb.2020.119652Get rights and content

Highlights

  • Biomass carbon foam synthesized by polymerization and carbonization of sucrose

  • Carbon foam as cathode possess excellent structural and electrochemical properties

  • Relatively good accumulation of electrogenerated H2O2 with the prepared cathode

  • Complete degradation and mineralization of sulfanilamide by EF oxidation with the cathode

  • Degradation and mineralization of sulfanilamide was influence by water matrices

Abstract

This work investigated, for the first time, the potential of novel biomass derived carbon foam as a suitable and efficient electrocatalytic material (as cathode) for in-situ hydrogen peroxide (H2O2) production and its applicability in electro-Fenton (EF) approach for oxidizing organic pollutants. The carbon foam cathode was prepared by polymerization and carbonization of sucrose at high temperature. The as-prepared carbon foam consists of highly porous and extremely light structure with interconnected spherical cells. It exhibited excellent electrocatalytic properties such as high conductivity, relatively high redox current and several active-sites for producing oxidizing species, such as H2O2. This demonstrated good electrocatalytic activity for in-situ production of H2O2, achieving up to 7 mg L‒1 at 60 mA. When carbon foam cathode was used in EF approach, it contributed to achieving complete degradation and COD removal of 0.5 mM synthetic sulfanilamide solution within 4 h of treatment. The EF process with carbon foam cathode also showed complete degradation and high mineralization of sulfanilamide in different electrolytes and real water matrices with extreme stability and reusability.

Introduction

The development of new materials or modification of the existing ones for efficient and enhanced in-situ selective two-electron reduction of dissolved oxygen for the electrogeneration of hydrogen peroxide (H2O2) is a key area of electrochemical advanced oxidation processes (EAOPs) based on Fenton’s chemistry, especially electro-Fenton (EF) process [[1], [2], [3]]. The H2O2 production rate at the cathode during electrolysis is the major parameter that controls the efficiency of the Fenton’s based EAOPs [1,[4], [5], [6]]. With optimum electrogeneration and catalytic decomposition of H2O2, Fenton’s based EAOPs are attractive and exciting technology for the remediation of synthetic and industrial effluents, especially those containing refractory organic pollutants that are highly resistant to conventional chemical oxidation and biological methods [[7], [8], [9], [10]]. Even though not fully commercialized owing to lack of technological license and scanty large-scale as well as the field-feasibility studies, the potential of this process is very huge and promising with higher possibility of commercial implementation in nearest future [10,11]. The fundamental principles, operational parameters and challenges of this process have been detailed in authoritative reviews and book chapters [1,[12], [13], [14]]. Briefly, reactive oxygen species mostly hydroxyl radicals (OH) are continuously produced in bulk solution during EF process from the reaction between on-site electrogenerated H2O2 and catalytic Fe2+ (Fenton’s reagent) (Eq. (1)) [[15], [16], [17]]. By careful selection of electrocatalytic material (as cathode), the Fenton’s reagents (H2O2 + Fe2+) can be continuously electrogenerated/regenerated via two electrons and an electron reduction of dissolved oxygen and Fe3+ (formed in Fenton’s reaction (Eq. (1)) at the cathode surface (Eq. (2) and (3)), respectively [1,18,19]. Therefore, the role of the cathode materials in Fenton’s based EAOPs cannot be over emphasized.H2O2 + Fe2+ + H+OH + Fe3+ + H2OO2 + 2e + 2H+ → H2O2Fe3+ + e → Fe2+

Among the existing cathode electrodes, carbonaceous materials such as carbon-felt [[20], [21], [22]], carbon sponge [3,23], carbon-fiber brush [24,25], carbon cloth [26] graphite/graphite felt [6,27,28] and gas-diffusion electrodes [1,[29], [30], [31], [32]] are the most widely studied electrodes in EF process due to their large surface areas and higher power for H2O2 generation, low cost and excellent electrical conductivity. However, researches are still on going to develop (by modifying existing materials) more inexpensive materials with higher H2O2 production efficiency, high stability and enhanced mineralization efficiency during EF oxidation of organic pollutants, as well as excellent environmental compatibility. Such advances have recently led to the use of pure and doped carbo-aerogels which have superior properties and efficiency compared to some other carbonaceous materials [7,33].

Carbon foam is an exotic porous solid material with an extremely light-weight that has open pores and high interior surface area. This material combines high porosity with relatively high strength and tunable thermal properties because the overwhelming majority of the volume in carbon foam is air [34,35]. Carbon foam has been majorly applied in thermal insulation, heat management systems, catalyst supports as well as electrodes in energy conversion, and storage and host structures for phase change materials [36,37]. Fossil fuel carbon based precursors such as coal tar and petroleum pitches are the initial materials used in preparing carbon foam, but the depletion of fossil fuel, combined with its environmental pollution and the need for natural renewable carbon source, has led to the use of biomass molecules such as tannin and sucrose as source of carbon for preparing carbon foams [34,38]. In general, there are four main steps involved in the preparation of carbon foams: (i) polymerization of the carbon precursors, (ii) blowing, (iii) setting and (iv) carbonization of the organic foam [34,38].

Based on the unique physicochemical properties of carbon foam especially its low density and high porosity, we envisage that these materials can be a good electrocatalytic candidate (as cathode) for efficient and effective oxygen reduction reaction and hydrogen peroxide (H2O2) production as well as application in electrochemical wastewater treatment technologies based on Fenton’s chemistry such as EF process.

On the other hand, sulfanilamide (4-aminobenzenesulfonamide) is a member of the larger group of drugs (antibiotics) called sulfonamides. Sulfanilamide has antibacterial activity and is widely used in human and veterinary medicine as well as in agriculture as herbicides [39]. High concentrations of sulfanilamide have been detected in different water bodies such as effluents of waste treatment plants, surface and ground waters [40]. Like other member of the sulfonamides group, it exhibits potential toxicity to aquatic organisms and is among drugs responsible for the emergence of antibiotic resistant strains [41]. Sulfanilamide is poorly biodegradable and as such, it is persistent in aquatic environment [40]. Sulfanilamide has been removed from aqueous solution by AOPs such as heterogeneous Fenton [42], photocatalysis [43], ferrate (VI) [44] sonocatalysis [45] and electrochemical technologies [46,47]; however, only electrochemical process using boron-doped diamond anode achieved excellent degradation and high mineralization efficiency [46,47].

Therefore, in this study we reported for the first time the application of biomass derived carbon foam for efficient on-site H2O2 production and its applicability as electrocatalytic material for EF oxidation of organic pollutants. The carbon foam was prepared by polymerization-blow-setting-carbonization technique using sucrose as carbon source. Physicochemical and electrochemical characterization using Scanning Electron Microscopy (SEM), Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and linear scanning voltammetry (LSV) were carried out on the prepared carbon foam. The electrocatalytic activity of the carbon foam, as cathode, for the production of H2O2 was tested and the applicability of this interesting material in EF process was investigated using sulfanilamide as the model organic pollutant. Real water samples were also electrochemically treated, and it demonstrated the efficiency of this material as cathode for producing H2O2, favoring EF approach for degrading organic pollutants. Finally, it is important to mention that the goal of this report is to propose as novel electrocatalytic-environmental material, the carbon foam, for emerging environmental-friendly advanced oxidation technologies.

Section snippets

Chemicals

Analytical grade of sucrose (99.5% purity; CAS: 57-50-1) and orthoboric acid (H3BO3) (99.8% purity; CAS: 10043-35-3) used as carbon source and blowing agent were obtained from Sigma Aldrich and used without further purification. Sulfanilamide (C6H8N2O2S) (99.5% purity; CAS: 63-74-1) used as model pollutant was supplied by Sigma Aldrich. Sodium sulfate (99.5% purity; CAS: 7757-82-6), sodium hydroxide (99–100% purity; CAS:1310-73-2), sulfuric acid (18.2 M) and potassium hexacyanoferrate (vi) (K3

Characterization

SEM images of the as-prepared carbon foam are shown in Fig. 1a-c. The carbon foam has cell structure with near spherical cells interconnected to each other via thin membranes [35,48]. Each spherical cell contains pores and a number of microcracks in the cell walls of the carbon foam which were initiated during the blowing step by the boric acid. Due to the number of the pores and micro cracks, the carbon foam structure is extremely light, highly rough and porous which can enhance the diffusion

Conclusions

The potential of carbon foam as a cathode material for on-site production of H2O2 and EF oxidation of organic pollution has been investigated. The prepared cathode was characterized by both structural and electrochemical techniques, before it was applied for electrolytic production of H2O2 and EF degradation of sulfanilamide as model organic pollutant. The prepared carbon foam performed excellently as cathode for electrosynthesis of H2O2 from dissolved oxygen and EF oxidation of organic

CRediT authorship contribution statement

Soliu O. Ganiyu: Formal analysis, Investigation, Methodology, Writing - original draft. Maria José Gomes de Araújo: Formal analysis, Investigation, Methodology. Emily C.T. de Araújo Costa: Investigation, Methodology. José Eudes Lima Santos: Formal analysis, Investigation, Methodology. Elisama Vieira dos Santos: Funding acquisition, Investigation, Data curation. Carlos A. Martínez-Huitle: Supervision, Conceptualization, Funding acquisition, Writing - review & editing. Sibele Berenice Castellã

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgement

Financial supports from Conselho Nacional de Desenvolvimento Científico e Tecnológico (Brazil) (CNPq – 439344/2018-2) and from Fundação de Amparo à Pesquisa do Estado de São Paulo (Brazil) (FAPESP 2014/50945-4 and 2019/13113-4) are gratefully acknowledged. Carlos A. Martínez-Huitle acknowledges the funding provided by the Alexander von Humboldt Foundation (Germany) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Brazil) as a Humboldt fellowship for Experienced Researcher

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