On the behavior of reduced graphene oxide based electrodes coated with dispersed platinum by alternate current methods in the electrochemical degradation of reactive dyes

Efficient photoelectrocatalytic degradation of azo-dyes over polypyrrole/titanium oxide/reduced graphene oxide electrodes under visible light: Performance evaluation and mechanism insights

Herein, polypyrrole/titanium oxide/reduced graphene oxide (PTi/r-GO) electrodes were prepared and successfully applied for the photoelectrocatalytic (PEC) degradation of methyl orange (MO) under visible light. Polypyrrole-TiO₂ composites rich in p-n heterojunctions were first prepared, then modified with r-GO to improve the electrical conductivity and facilitate charge separation under visible light irradiation. The obtained PTi/r-GO composites were then deposited onto a titanium mesh, which served as the working electrode in PEC experiments. A MO removal efficiency of 93% was achieved in 50 min using PTi/r-GO electrode under PEC conditions (Xe lamp, λ > 420 nm, bias of 0.6 V, 0.1 M Na₂SO₄ electrolyte), which was far higher than MO removal efficiencies under electrocatalytic oxidation (22%) or photocatalytic oxidation (47%) conditions. This confirmed that excellent activity of the PTi/r-GO electrode under PEC conditions was due to a combination of electrochemical and photocatalytic oxidation processes (involving •OH and •O₂^- generation). Further, PTi/r-GO was very stable under the applied PEC conditions, with the MO removal efficiency remaining >90% after five cycles. PEC degradation pathways for MO on PTi/r-GO were explored, with a number of key intermediates in the MO mineralization process identified. Results demonstrate that PEC electrodes combining p-type polypyrrole, n-type TiO₂ and rGO are very effective in the treatment of hazardous organic compounds in wastewater.

Effect of chloride on the one step electrochemical treatment of an industrial textile wastewater with tin dioxide anodes. The case of trichromy procion HEXL

The resulting solutions from the cotton fabrics dyeing using the trichromy Procion HEXL, with NaCl as electrolyte, were electrochemically treated. These dyes have two azo groups as chromophores and two monochlorotriazinic groups as reactive groups in their structure. The combined oxidation/reduction at 125 mA cm^-2 in a filter-press cell without compartment separation was carried out using an anode of Ti/SnO₂-Sb-Pt and a cathode of stainless steel. This procedure has been effective in previous experiments using sulphate as electrolyte. A significant decrease in total organic carbon (TOC), chemical oxygen demand (COD), and total nitrogen (TN) was obtained. Moreover, the process took place efficiently. The average oxidation state (AOS) and the carbon oxidation state (COS) data confirmed the presence of stable oxidized intermediates in the electrolysed solution. The chromatography and the UV-Visible spectrophotometry assays indicated that full decolourisation is obtained at a loaded charge of around 0.81 Ah L^-1 which is associated with an electrical energy per order (EEO) of 1.20 kWh m^-3.

Soybean Peroxidase Catalyzed Decoloration of Acid Azo Dyes

BACKGROUND

Some industrial manufacturing processes generate and release dyes as water pollutants, many of which are toxic and hazardous materials. There is a need for milder, greener methods for dye treatment.

OBJECTIVES

The objective of the present study was to investigate and optimize azo dye decoloration by a crude soybean peroxidase (SBP), based on two dyes that have widespread industrial use, but that differ greatly in structural complexity, Acid Black 2 and Acid Orange 7, and to investigate the effects of specific parameters on the removal process.

METHODS

Batch reactors were used to remove 95% of the dyes' color and to produce substantial precipitates.

RESULTS

The optimum pH for enzymatic decoloration of Acid Black 2 was in the acidic region, pH 4.4, and that of Acid Orange 7 occurred under neutral conditions, pH 6.9. The minimum enzyme activity needed for sufficient removal was 1.2 U/mL for both dyes at 0.5 mM. The minimum molar hydrogen peroxide/substrate ratio was 3 for Acid Orange 7 and 2.5 for Acid Black 2 to achieve approximately 95% removal. First-order fitting of progress curve data collected under the respective optimum conditions gave half-lives of 23.9 and 28.9 minutes for Acid Orange 7 and Acid Black 2, respectively.

CONCLUSIONS

The feasibility of SBP-catalyzed treatment of industrial dyes Acid Black 2 and/or Acid Orange 7, or dyes that resemble them, as they might occur in industrial effluents, was successfully demonstrated.

COMPETING INTERESTS

The authors declare no competing financial interests.

Co nanoparticle-embedded N,O-codoped porous carbon nanospheres as an efficient peroxymonosulfate activator: singlet oxygen dominated catalytic degradation of organic pollutants

A mesoporous N,O-doped carbon@Co composite with good magnetism for efficient catalytic elimination of organic pollutants via peroxymonosulfate activation.

Silkworm cocoon derived N, O-codoped hierarchical porous carbon with ultrahigh specific surface area for efficient capture of methylene blue with exceptionally high uptake: kinetics, isotherm, and thermodynamics

Dyes are typical water contaminants that seriously affect water quality. In this study, silkworm cocoon derived N, O-codoped hierarchical porous carbon was successively developed via a facile pre-carbonization and chemical activation method, and characterized thoroughly by SEM, TEM, HRTEM, XRD, Raman, N₂ adsorption and XPS. The as-prepared N, O-HPC showed a well-developed porous structure with an ultra-high specific surface area of 2270.19 m² g^-1, which proved to be a high-efficiency adsorbent. Batch adsorption experiments demonstrated that MB adsorption was highly dependent on contact time, initial MB concentration, temperature and initial solution pH. However, no remarkable effects of humic acid and ionic strength were observed. In the kinetic studies, the good applicability of a pseudo-second-order kinetic model was demonstrated. The adsorption isotherm study showed that a Langmuir isotherm model can describe the experimental data much more suitably with a maximum monolayer adsorption capacity value of 2104.29 mg g^-1, which is among the highest in previously reported adsorbents and ascribed to multiple adsorption mechanisms including pore filling, π-π stacking interaction and electrostatic interaction between MB and N, O-HPC. Thermodynamic analyses suggested that MB adsorption onto N, O-HPC was spontaneous and endothermic. Furthermore, the as prepared adsorbent showed highly efficient adsorption for MB in tap water and synergistic adsorption performance toward MB and MO. Therefore, N, O-HPC derived from silkworm cocoon could be considered as an efficient, novel and advantageous material for wastewater remediation.

One-step reducing and dispersing graphene oxide via hydroxypropyl hydrazine and its applications in Cu2+ removal

Graphene is widely used in numerous scientific fields including physics, chemistry and materials science due to its exceptional electrical, thermal, optical and mechanical properties. However, the poor solubility/dispersibility strongly limits the practical applications of graphene. In this work, hydroxypropyl hydrazine (HPH) was synthesized to reduce graphene oxide (GO) under mild conditions. The as-produced graphene sheets with a 3D-porous structure show admirable dispersion stability in N,N-dimethylacetamide (DMAc) and the graphene sheets are more effective absorbents for Cu²⁺ removal than those reduced by hydrazine hydrate. A mechanism for removal of epoxides and carboxides from GO by HPH has been proposed. This one-step reducing and dispersing process of GO is more efficient, environmentally benign and safer for the bulk-scale production of 3D porous graphene.