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This theoretical investigation delves into the analysis of Reactive red 2 (RR-2) adsorption isotherms on metal hydroxide employing a sophisticated double-layer model characterized by dual-energy levels within the realm of physical adsorption phenomena. An examination of five distinct statistical physics frameworks was undertaken to elucidate the modeling and interpretation of equilibrium data. Expression for the physico-chemical parameters involved in the adsorption phenomena was derived based on statistical physics treatment. Fitting experimental adsorption isotherms (308-333 K) to a DAMTBS has revealed the number of anchored molecules per site, occupied receptor site density, and the number of adsorbed layers. The steric parameter n varies between 0.92 and 1.05. More importantly, it is evidenced that the adhesion mechanism of (RR-2) onto metal hydroxide as determined by the estimated adsorption energies (< 40 kJ/mol) supports a spontaneous and exothermic physisorption process. Thermodynamic potential functions such as entropy, Gibbs free energy, and internal energy have been computed based on the most suitable model. This research advances our physical understanding of how metal hydroxide captures dye molecules RR-2 through adsorption reaction for water depollution treatment.

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The current study involves a synthesis of a composite of nickel oxide nanoparticles (NiONPs) with a chromium dopant to yield (Cr/NiONPs). Synthesis of nickel oxide was performed by the co-precipitation method. The synthesis of the composite was conducted by the impregnation method. FTIR, EDX, SEM, and XRD were used to characterize the synthesized materials. The synthesised materials' point zero charges (PZC) were performed using the potentiometric titration method. The obtained results show that the PZC for neat nickel oxide was around 5, and it was around 8 for Cr/NiONPs. The adsorption action of the prepared materials was examined by applying them to remove Reactive Red 2 (RR2) and Crystal Violate (CV) dyes from solutions. The outcomes demonstrated that Cr/NiONPs were stronger in the removal of dyes than NiONPs. Cr/NiONPs achieved 99.9% removal of dyes after 1 h. Adsorption isotherms involving Freundlich and Langmuir adsorption isotherms were also conducted, and the outcomes indicated that the most accurate representation of the adsorption data was offered by Langmuir adsorption isotherms. Additionally, it was discovered that the adsorption characteristics of the NiONPs and Cr/NiONPs correspond well with the pseudo-second-order kinetic model. Each of the NiONPs and Cr/NiONPs was reused five times, and the results display that the effectiveness of the removal of RR2 dye slightly declined with the increase in reuse cycles; it lost only 5% of its original efficiency after the 5 cycles. Generally, Cr/NiONPs showed better reusability than NiONPs under the same conditions.

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Owing to their surface active properties, surfactants have numerous applications in different fields of life. In the present research work, the solubilization of reactive red 2 (RR2) has been studied in single and mixed micellar systems (MMS) using UV-visible spectroscopy and electrical conductivity measurements. The interaction of RR2 with ionic micelles of cetylpyridinium chloride (CPC) was investigated. In order to probe the interaction of RR2 in MMS, mixtures of CPC and TX-114 (Triton X-114, a nonionic surfactant) were used. UV-visible spectroscopy has been used to obtain the degree of solubilization of RR2 in terms of the partition coefficient (Kc) and Gibbs free energy of partitioning (ΔG°p). Electrical conductivity data have been employed to detect the critical micelle concentration (CMC) of the surfactant systems in the presence of RR2 and, accordingly, to calculate the thermodynamic parameters of the micellization. From the obtained data, it is concluded that the micellization is spontaneous at all studied temperatures. Moreover, the micellization was observed to be driven by both enthalpy and entropy. The results also indicated that MMS have better solubilizing power than single micellar solutions.

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Reactive red 2 (RR2) azo dye wastewater poses a serious hazard to the water environment health, so using a novel and efficient Electro- Ce(III) (E- Ce(III)) process takes on a critical significance in treating RR2 dye wastewater. In this study, the effects of a variety of single-factor conditions on RR2 removal efficiency were evaluated in depth. The results indicated that the optimal experimental conditions are as reaction temperature of 25 °C, Na2SO4 concentration of 25 mM, Ce(III) concentration of 0.3 mM, pH of 4.0, and current density of 40.0 mA/cm2. When the RR2 dye wastewater was treated for 40 min under the optimal experimental conditions, a high removal rate of 99.8% for RR2 was obtained. It is suggested that the background ion PO43- in the dye wastewater inhibits the E-Ce (III) process, whereas Cl- facilitates this process. Moreover, the yield of Ce(IV) increases with the increase of the current density. At the current density of 40.0 mA/cm2, a reasonable energy consumption of 3.85 kW h/gTOC for the process was obtained after the 3-h treatment. The effects of different degradation processes (including Direct Electrooxidation (DEO), single Ce(III), and E-Ce (III)) on RR2 removal efficiency and TOC change were compared. The types of oxidizing substances in the E-Ce (III) process were detected, and the mechanism of RR2 oxidative degradation in the E-Ce (III) process was summarized. The result suggests that the E-Ce (III) process has low power consumption. Meanwhile, in the E-Ce (III) process, free reactive Ce(IV) with strong oxidation is continuously generated, RR2 can be efficiently degraded. And the continuous cycle transformation between Ce(III) and Ce(IV) maintains the strong oxidation of the process. The contribution of free reactive Ce(IV) and DEO to RR2 degradation was obtained as 58.8% and 39.8%, respectively. The combined effect of Ce(IV) and DEO played a major role in the E-Ce (III) process, while ·OH exhibited a relatively weak effect (nearly 1.4%). RR2 was comprised of 13 major intermediates, and the biodegradability of wastewater was improved significantly after treatment, thus facilitating the further mineralization and biodegradation of the products. The E- Ce(III) process is novel, efficient, and environment-friendly, and has a large market application space, suggesting that it can be applied as an efficient, economic, and sustainable water treatment process.

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Reactive red 2 (RR2) is a highly recalcitrant and toxic azo dye that can cause the collapse of biological treatment system. Although MFC can decolorize RR2 effectively, its performance is still inevitably affected by toxicity. Anthraquinone can enhance MFCs' performance through mediating electron transfer. In this study, an anthraquinone-rich natural plants (B.rheum (Rheum offcinale Baill)) was extracted and then added to MFCs. The optimal dosage was selected and the enhanced effects were investigated. The results showed that adding 5%(V/V) extract resulted in the optimal performance elevation of MFC. When 5% extract was added together with RR2, 15.63% and 1.33-fold improvement in RR2 decolorization efficiency and rate were achieved compared with the control group. Meanwhile, higher power density (2.75 W/m3), coulombic efficiency (6.45%), and lower internal resistance (233.69 Ω) were also observed when 5% B.rheum extract and RR2 were added. B.rheum extract in MFCs enhanced microbial activity and enriched the dye-degrading microorganisms, such as Enterobacter, Raoultella, Comamonas and Shinella. B.rheum extract acts as "antidote" in alleviating the biotoxicity of RR2 was firstly illustrated in this study. The results provided a new strategy for using plant-source electron mediators to simultaneously improve biological detoxification, bioelectricity generation and dye decolorization in bioelectrochemical system.

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A facile one-step pyrolysis method was employed to prepare an iron containing carbonaceous catalyst using coagulation waste (CW) from paper mill. The catalyst (noted as PMCW) was used to activate peroxymonosulfate (PMS) for decomposition of Reactive Red 2 (RR2). The degradation mechanism was analyzed by reactive oxygen species (ROS) scavenging experiments, electron spin resonance spectroscopy, electrochemical measurements, selective deactivation of the functional groups on the catalyst surface, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Results showed that, besides ROS (•OH, SO4•- and 1O2), electron transfer pathways induced by -OH functional groups and the π-π* system are involved in the degradation mechanism of RR2. Concerning different decomposition pathways, seven intermediates were identified, and three important steps, including attack on the azo group, cleaving the N9-C10 bond, and opening the naphthalene ring, were deduced via application and analysis of quadrupole time-of-flight liquid chromatography/mass spectrometry (QTOF LC/MS) and density functional theory (DFT) calculations based on Fukui indices and electrostatic potential (ESP) distributions. This work not only provides a novel facile recycling strategy of industrial waste from paper manufacturing to good carbonaceous catalysts but also deepens the understanding of the mechanisms of PMS activation with carbonaceous materials.

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In this work, anthraquinone-2-sulfonate (AQS) was covalently immobilized onto activated carbon cloth (ACC), to be used as redox mediator for the reductive decolorization of reactive red 2 (RR2) by an anaerobic consortium. The immobilization of AQS improved the capacity of ACC to transfer electrons, evidenced by an increment of 3.29-fold in the extent of RR2 decolorization in absence of inhibitors, compared to incubations lacking AQS. Experiments conducted in the presence of vancomycin, an inhibitor of acidogenic bacteria, and with 2-bromoethane sulfonic acid (BES), an inhibitor of methanogenic archaea, revealed that acidogenic bacteria are the main responsible for RR2 biotransformation mediated by immobilized AQS. Nonetheless, the results also suggest that some methanogens are able to maintain their capacity to use immobilized AQS as an electron acceptor to sustain the decolorization process, even in the presence of BES.

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The application of immobilized redox mediators (RMs) in microbial fuel cells (MFCs) is an emerging technology for electricity generation with simultaneous azo dye decolorization due to facilitated electrons transfer from bacteria to anodes and azo dyes. The use of immobilized RMs avoids the requirement of their continuous dosing in MFCs, which has been the main limitation for practical applications. Two strategies of anthraquinones-2,6-disulphonic salt (AQDS) immobilization, AQDS immobilized with polyvinyl alcohol particles and AQDS immobilized on anodes by electropolymerization, were evaluated and compared to achieve simultaneous reactive red 2 (RR2) dye reduction and bioelectricity generation. The AQDS immobilized by electropolymerization showed the highest power density (816±2mW/m2) and extent of RR2 decolorization (89±0.6%). This power density is one of the highest values yet achieved in the presence of a recalcitrant pollutant, suggesting that immobilization was important for enabling current generation in the presence of RR2.

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This study was undertaken to prepare a novel and environmentally friendly composite for the use in the wastewater treatment process. This composite was produced by immobilizing alunite with a glucosamine biopolymer, chitosan. Batch and dynamic flow mode decolorization potential of the chitosan-alunite composite (CAC) was systematically evaluated in Acid Red 1 (AR1) and Reactive Red 2 (RR2) contaminated media. pH, sorbent dosage, contact time and flow rate were screened through the sorption experiments. Equilibrium sorption experiments indicated that CAC has very high sorption potential for RR2 and AR1 dyes with the maximum sorption capacities of 462.74 and 588.75 mg g(-1), respectively. Good regeneration and reuse potential in 20 consecutive cycles are other important advantages of this composite. More importantly, CAC could also be used in the treatment of real wastewater without performance decrease. Overall, this study suggests that CAC is a promising sorbent for the removal of anionic dyes from aqueous solutions.

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Sludge from the textile industry was used as a low-cost adsorbent to remove the dye Reactive Red 2 from an aqueous solution. Adsorbents were prepared through the thermal and chemical treatment of sludge originating from physical-chemical (PC) and biological (BIO) effluent treatment processes. The adsorbent characterization was carried out through physical-chemical analysis, X-ray fluorescence (XRF) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, pHPZC determination, Boehm titration method, Brunauer-Emmett-Teller (BET) surface area analysis and scanning electron microscopy (SEM). Batch kinetic experiments and adsorption isotherm modeling were conducted under different pH and temperature conditions. The results for the kinetic studies indicate that the adsorption processes associated with these systems can be described by a pseudo-second-order model and for the equilibrium data the Langmuir model provided the best fit. The adsorption was strongly dependent on the pH but not on the temperature within the ranges studied. The maxima adsorption capacities were 159.3 mg g(-1) for the BIO adsorbent and 213.9 mg g(-1) for PC adsorbent at pH of 2 and 25 °C.

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