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4-chlorophenol (4-CP) is recognized as a highly toxic organic which can cause damage effects on human life and the aquatic environment. Since conventional wastewater techniques were unable to remove non-biodegradable chlorophenols, advanced oxidation process was investigated to achieve this goal. Amongst them, non-thermal plasma was recently proposed as an alternative and promising technique. However, the energy efficiency of most non-thermal plasma technique is very low as well as the input energy is dissipated in many forms such as heat, UV radiation, electromagnetic waves, etc., that are not totally involved in the pollutant degradation. In this work, quantitative analyses of UV radiation and H2O2 in a moist air gliding arc plasma (glidarc) were performed using potassium ferrioxalate actinometry and peroxytitanyl complex method, respectively. The role of UV light emitted in gliding arc plasma was elucidated by performing parallel experiments: H2O2, glidarc alone, glidarc + H2O2, glidarc + H2O2 + Fe3+ (plasma-Photo-Fenton). The results show that the incorporation of Fenton reagents in 4-CP solution exposed to the plasma enhanced the yields of chemical active species, which were available for efficient removal and mineralization of 4-CP.

Nanostructured metal oxides are good candidates for applications in heterogeneous catalysis. Recently our consortium has developed the preparation of such materials by exploiting the redox properties of the non-thermal gliding arc plasma (glidarc) in humid air. This contribution aims at sharing with the community active in the field of heterogeneous catalysis that the glidarc technique is an easy and accessible, but powerful technique with a very bright future that can be used for producing heterogeneous oxide catalysts. Therefore, we present here our most recent achievements in the preparation of titanium, iron and manganese oxide catalysts using glidarc. TiO2 nanorods containing both rutile and anatase phases with improved photocatalytic activity under visible light were obtained by oxidizing Ti3+ ions in aqueous solution with the plasma species. Fe2+ ions exposed to the plasma discharge were transformed into sea-urchin-like porous goethite (α-FeOOH) nanostructures via the consecutive oxidation-hydrolysis processes. The synthesized goethite was mesoporous with a high surface area. Clay supported catalysts were also prepared by depositing the goethite particles on kaolinite. Those catalysts (and their calcination products) were active in heterogeneous Fenton degradation of organic dyes. α-MnO2 nanorods were obtained by a rapid reduction of MnO4− ions after exposing an aqueous solution of potassium permanganate to the plasma discharge.

In this study, laterite soil containing various mineral oxides (e.g., Al2O3, Fe2O3 and TiO2), used as an alternative catalyst, was combined with gliding arc plasma treatment for Orange G (OG) degradation in aqueous solution. The results showed that the incorporation of laterite soil (as catalyst) in (OG solution exposed to plasma led to a significant degradation enhancement from 17% for plasma treatment alone to almost 100%. Compared with P25 TiO2, Fe2O3, and TiO2/Fe2O3 photocatalysts, the decolorization rate of OG can be increased from 56, 68 and 75% respectively to 100% after 60 min laterite-mediated plasma treatment. In the calcinated laterite, Fe2O3 was considered not only as TiO2 sensitizer due to its narrow band-gap but also as the heterogeneous Fenton catalyst. These synergistically enhanced the generation of the reactive species, i.e., OH, in the gliding arc plasma system and thus process efficiency for OG removal. Under optimized operating conditions, approximately 83% mineralization of OG solution was achieved within 60 min of treatment with the combined process. From the kinetics point of view, OG oxidation fitted with Langmuir–Hinshelwood model with the second-order rate constant (kr) and adsorption constant (Ks) of 5.74 mg min−1 and 0.12 L mg−1, respectively, suggesting that the reaction occurs at the catalyst surface. The catalyst was highly stable even after 5 consecutive cycles.

This work presents the treatment of an organic waste solution using gliding arc plasma in moist air, which is an excellent source of oxidizing species. Herein particular attention is devoted to the comparative energy balance between two model reactors in order to optimize the process and get closer to a large-scale application. The model pollutant Amoxicillin is an antibiotic agent largely used against allergies and has been found in wastewaters. Its degradation is studied by exposing basic solutions to underline the role of the formed •OH radicals and H2O2 reactive species. The degradation of AMX to give CO2, H2O, and sulfate is optimized within 120 min with a resulting abatement of 78% and 98% for batch and circulation reactors respectively. The kinetic study suggests a pseudo-first order process with an apparent rate constant three times higher in circulation mode compared to batch mode reactor. Accordingly, the energetic yield is 2.5 times better in the circulation system, owing to more consumption of plasma-generated species with respect to the high reactive area, whereas in batch mode reactor, AMX degradation is occurred at the plasma-liquid interface, and thus limited by the mass transfer process.

The reason that some molecules, but not others, are easily adsorbed was not fully understood. In order to spotlight the effect of morphological structure and surface functional composition of adsorbate rather than focusing only on the nature of adsorbent as in most of literature reports, this work reports the biosorption of two dyes (anionic Orange G and cationic malachite green) and two pharmaceuticals (Ibuprofen and ampicillin) as target representative contaminants onto plasma-modified cocoa shell (CPHP) used as alternative low-cost adsorbent. As results, when molecules were mixed in solution and then exposed to a substrate, the factors that affect adsorption include the relative solvation of the adsorbates, the ability of each molecule to adhere to the surface, and the degree of interaction between the molecules once they were adsorbed. The maximum adsorbed amounts at 298 K of OG, MG, IBP, and AMP were 23.96, 14.65, 13.99, and 06.66 mg/g, respectively. The most solvated molecules may not adsorb rapidly to the surface, while comparatively, the less soluble molecules will aggregate, so as to maximize self-interactions via Van der Waals, hydrogen bonds or other interactions. This work demonstrated that the adsorbate intrinsic properties could play a significant role in the adsorption process. Hence, properties such as functional active groups, dimensions, and hydrophobicity were the determining parameters in the adsorption process mechanism. Accordingly, the pharmaceuticals biosorption mechanism involved π-π bonding, hydrophobic effect, electrostatic interaction, and van der Waals forces whereas the dye biosorption mechanism was dominated as well known by electrostatic attraction and hydrogen bonding phenomenon. Experimental parameters such as initial pH of solution and contact time were optimized. The optimum pH values were 2.0 for ibuprofen (IBP) and 7.0 for ampicillin (AMP). The kinetics of adsorption and the experimental isotherms data were analyzed using non-linear models. Results indicated that Avrami fractional order was the most successfully fitted model for pharmaceutical biosorption and based on the statistical values of SD and R2adj parameters, Liu isotherm was the most successfully fitted model.

Textile effluents containing synthetic dyes are one of the most important sources of water pollution. Several dyes are toxic to the aquatic life and indirectly to humans, and therefore should be treated before rejection to natural water streams. As conventional wastewater treatment systems remain inefficient for treatment of these recalcitrant pollutants, the use of advanced oxidation processed is required. The degradation of the Orange G dye was studied using the photo-Fenton process. Results showed that the use of experimental kinetics rate constants to optimize the ratio R = [H2O2]/[Fe3+] constitutes a suitable way to minimize the occurrence of side reactions. An optimal molar ratio R of 13.8 was found allowing complete degradation of Orange G in 4 min and 93.41% total organic carbon (TOC) removal in 180 min. Based on detected intermediates and end-products, a plausible degradation mechanism of Orange G dye is proposed. Therefore, we demonstrated that the photo-Fenton process can be applied efficiently to the removal of toxic/persistent organic pollutants such as synthetic dyes from water.

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This study reports the tailoring of surface chemistry of palm fibers via plasma for the adsorption of sodium diclofenac from aqueous solution. Surface functionalization of palm fibers was carried out with three feeding gases: humid air, air saturated with hydrogen peroxide and air saturated with sodium hydroxide. Functionalized palm fibers were physicochemical characterized and their diclofenac adsorption properties were compared. Diclofenac adsorption tests were performed at different operating conditions (initial concentration, particle size, pH and temperature). Kinetics and isotherms of the diclofenac adsorption on raw and plasma-based functionalized fibers were quantified and modeled with different equations. Thermodynamic parameters of diclofenac adsorption were estimated and statistical physics calculations were carried out to characterize the adsorption orientation of diclofenac molecules on biomass surface. Overall, the palm fibers functionalized with plasma and hydrogen peroxide showed the best adsorption properties for the removal of this pharmaceutical. Results showed that diclofenac adsorption was a multi-molecular exothermic process with an inclined adsorption orientation on the fiber surface. The experimental maximum adsorption capacities decreased from 33.12 to 24.71 mg/g at 25–50 °C. Liu model provided the best correlation of experimental data for all adsorption temperatures. Solution pH played a relevant role in the diclofenac adsorption mechanism where hydrogen bonding, van der Waals forces and electrostatic interactions were involved. This paper contributes to the valorization of biomasses for implementing low-cost and effective adsorption processes to face the water pollution caused by pharmaceuticals.

Removal of cationic dye, Azur II, and anionic dye, Reactive Red 2 (RR-2) from aqueous solutions, has been successfully achieved by using a modified agricultural biomaterial waste: cocoa shell husk (Theobroma cacao) treated by gliding arc plasma (CPHP). The biomass in its natural form CPHN and modified form CPHP was characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and point of zero charge (pHpzc). Experimental variables such as initial pH, contact time, and temperature were optimized for adsorptive characteristics of CPHN and CPHP. The results show that the removal of the Azur II dye was favorable in the basic pH region (pH 10) while the Reactive Red 2 dye was favorable in the acidic pH region (pH 2). The minimum equilibrium time for Azur II and RR-2 dye was obtained after 40 and 240 min, respectively. The adsorption kinetics and isotherm data obtained were best described by a pseudo-second-order kinetic rate model and a combination of Langmuir-Freundlich isotherm models. This work indicates that the plasma-treated raw materials are good alternative multi-purpose sorbents for the removal of many coexisting pollutants from aqueous solutions.

Manganese (IV) oxide (MnO2) nanoparticles were synthesized, via a plasma-chemical route by using a gliding arc discharge at atmospheric pressure. α-MnO2 nanorods were obtained from the chemical reduction of KMnO4. The synthesis yield was 96.8% after 4.5 min of exposure of the solution to the plasma. Further increase of the exposure time induced a decrease of MnO2 yield because of its reductive transformation into Mn2+ ions. Particles were characterized by X-ray powder diffraction, scanning electron microscopy, Fourier Transform Infrared spectroscopy, and nitrogen physisorption. The plasma-catalytic properties of the synthesized material were tested in the bleaching of amaranth red (AR). AR bleaching efficiencies of 17 and 44% were respectively obtained when the plasma and plasma-catalyst processes were applied for 30 min with initial pH 10. The influence of the initial pH, and catalyst concentration were investigated: the AR bleaching efficiency increased linearly with the catalyst concentration and increased markedly when the pH of the solution decreased.

A Cameroonian kaolinite powder was treated with gliding arc plasma in order to increase the amount of hydroxyl functional groups present on its external surfaces. The functional changes that occurred were monitored by Fourier transform infrared spectroscopy. The crystalline changes were followed by the X-ray diffraction. The ionisation effect, acid effect, and water solubility of the treated samples were also evaluated. Results showed that there is breaking of the bonds in the Si–O–Si and Si–O–Al groups, followed by the formation of new aluminol (Al–OH) and silanol (Si–OH) groups at the external surface of kaolinite after exposing the clay to the gliding arc plasma. The increase in hydroxyl groups on the surface of kaolinite leads to the increase of its hydrophilicity. Moreover, new charges appear on its surfaces and no significant change in crystallinity has occurred. This study shows that clays in powder form being can effectively be functionalised by gliding arc plasma in spatial post discharge processing mode. Knowing that the treatment in spatial post discharge offers the possibility to process large amounts of clay, this work is of great interest to the industry.

A plasma-assisted synthesis of TiO2/SnO2 nanocomposite is described. In this approach, a precursor containing a mixture of [TiCl3 and SnCl2] exposed to electric discharge was oxidized by plasma-generated reactive species (HO·/H2O = 2.85 eV/SHE). SnO2 microstructures with a diameter of 10–40 µm were coated by thin layers TiO2 nanorods with mean diameter of 6–8 nm. The obtained TiO2/SnO2 nanocomposite was characterized by transmission and scanning electron microscopy, X-ray diffraction and Fourier transform infrared. TiO2/SnO2 nanocomposite was found to be a promising new material for the photocatalytic discoloration of aqueous Remazol Brilliant Blue-R dye under daylight and UVA light sources, due to the combined effects of large specific surface area and heterojunction which efficiently separates the electron–hole pairs delaying the charge recombination. The leaching test indicated that the nanocomposite is stable easily reusable.

This study investigates the ability of spatial post-discharge mode functionalized kaolin to remove textile dye Reactive Red 2 from aqueous solution compared to that of the raw kaolinite. To fulfill the aim, the removal conditions, including plasma exposure time, processed mode (direct and post-discharge), pH of the aqueous dye solution, initial dye concentration and adsorbent dosage, were investigated. The changes that occur on clay surfaces before and after gliding arc plasma treatment were followed by Fourier transform infrared spectroscopy, scanning electron microscopy and nitrogen physisorption. The point of zero charge and the changes of the textural properties after gliding arc plasma treatment were also examined. The experimental data were analyzed using pseudo-first-order, pseudo-second-order and empirical Elovich models. The diffusion phenomenon was also studied. The results obtained indicate that spatial post-discharge pre-treatment of kaolin deeply influences the functional groups of some of its minerals as well as the morphology and texture of its particles. Consequently, at room temperature (∼30 °C), the maximum adsorption capacities of natural raw kaolin clay were tripled after treatment with gliding arc plasma in spatial post-discharge mode and were almost doubled after the direct treatment mode.

The exposure of TiCl3 to the plasma electric discharge burned in moisten air lead to the formation of TiO2 nanopowder for short exposure time (

Wastewater samples from liquid effluents of cotton oil refinery in Far-Northern Cameroon were exposed to a gliding arc discharge for various exposure times in a cold plasma reactor. The analysed results showed high levels of organic pollution parameters (TOC = 4635 mg/L, COD = 6943, 98 mg/L) before treatment. More than 56% TOC and 75% COD abatement were obtained after 30 min treatment in batch conditions with a laboratory reactor. The resultant pollution abatement is attributed both to strong oxidizing effects of °OH and NO° radicals formed in the plasma and their derivatives (H2O2, ONO2H and NO3H). The conductivity and TDS increase linearly and the pH, TOC and COD decrease with increasing exposure time to the discharge. The oxidation obeys a pseudo first-order kinetics law (kinetic rate: k1DCO = 0, 0381 min−1 and k1COT = 0, 0245 min−1).

The degradation of simulate house effluent containing Nitrophene and Glycine was carried out using gliding arc plasma reactor, one of the upcoming advance oxidation techniques. Aiming to reduce energy cost of treatment, the effect of various parameters such as treatment time, post-discharge phenomenon and addition of Jatropha natural biomass have been discussed. The experiments were conducted at a gas flow rate of 800 L/h. The degradation rate depends on the flow of highly oxidizing species formed in the plasma arc and on the sorbent/liquid contact surface time. Furthermore, the kinetic process of the in-situ treatment follows the pseudo-first order model while the post-discharge phenomenon is governed by the general order kinetic model. The initial high polluted solution with 950 mg/L TOC is degraded to 658 mg/L as final TOC after 1 h of in-situ treatment and to 460 mg/L TOC after 6 h in post-discharges. The use of Jatropha shell as biosorbent in addition of the plasma treatment reduces the TOC from 950 to 530 mg/L for in-situ treatment and, to 280 mg/L after 6 h in post-discharge. These results have showed that it is possible to significantly improve the efficiency of plasma treatment by incorporating modified agricultural residues. The occurrence of CO2 is detected during the plasma treatment by Drager tube analyser, while N O 2 − and N O 3 − are also identified by colorimetric tests.

This study focuses on the discolouration of a triphenylmethane dye (ie methyl violet 10B) using a gliding arc plasma discharge in humid air. The results show that the discolouration process is strongly dependent on the initial dye concentration. The maximum discolouration rates are 96.9% and 6.7% after 60 min for initial dye concentrations of 2.5 mg L− 1 and 100 mg L− 1, respectively. The incorporation of maghemite (γ-Fe 2 O 3) into a 100 mg L− 1 dye solution increases the discolouration rate under plasma up to 55.6%. This improvement of the discolouration efficiency suggests that maghemite acts as a heterogeneous catalyst for Fenton decomposition of H2O2 resulting from the dimerization of HO radicals produced by plasma in the gas phase. The X-ray diffraction (XRD)and Fourier transform-infrared(FTIR)characterizations of the catalyst before and after being used 3-times show that the maghemite nanoparticles are stable in the target-solution exposed to gliding arc plasma and can be therefore reused for further treatments.

Smectite clay from Sabga (west-Cameroon) was treated in aqueous suspension by gliding arc plasma to modify its surface properties. The evolution of the modifications was followed with the exposure time and post-discharge duration using Fourier transformed infra red spectroscopy and scanning electron microscopy. X-ray diffraction and nitrogen physisorption analyses were also performed to evaluate if both crystalline and textural properties of the material are affected by the treatment. The results obtained show that the plasma treatment causes the breakdown of structural bounds at the clay surface and induces the formation of new hydroxyl groups (Si–OH and Al–OH) on the clay edges. Crystallinity, sheet structure and textural properties are not significantly affected by the plasma treatment. However, it should be noted that an intensive treatment of the clay lowers the pH of the suspension, which subsequently induces an acid attack of the clay. In such case, the specific surface area of the clay increases. This study demonstrates that gliding arc plasma treatments can be used to activate clay minerals for environmental application.

The aqai palm stalk (Euterpe oleracea) is food residue used in its natural form (AS) as biosorbent for the removal of Evans Blue (EB) and Vilmafix Red RR-2B (VR) textile dyes from aqueous solutions. The effects of pH, biosorbent dosage, and shaking time on biosorption capacities were studied. The maximum adsorption of both dyes occurred at pH 2.0. The Avrami fractional-order kinetic model provided the best fit to experimental data compared with pseudo-first-order and pseudo-second-order kinetic adsorption models. The equilibrium data were fitted to Langmuir, Freundlich, and Sips isotherm models. For both dyes, the equilibrium data were best fitted to the Sips isotherm model. Simulated dyehouse effluents were used to check the applicability of the proposed AS biosorbent for effluent treatment.

Chemical coagulation and adsorption, despite many drawbacks, are actually the main techniques used for the removal of pollutants from aqueous solution; however, these techniques are becoming ineffective due to the exponential increase in the amount and complexity of discharged pollutants; thus, the sludge treatment process became a more complex challenge. The present study focuses on the way to reduce the quantity of sludge formed during the removal of Ridomil Gold, a widely used pesticide-fungicide in agriculture. Results revealed that pre-treatment of initial waste solution by the gliding arc (Glidarc), a source of non-thermal plasma, leads to a significant reduction of the sludge formed during the coagulation treatment. For a 20-min pre-treated effluent Glidarc followed by chemical coagulation, there was a reduction in the volume of sludge formed in the order of 90 and 80% for alum and ferric sulfate coagulants respectively without reducing the performance of pesticide removal. Therefore, there is a positive synergism between treatment by chemical coagulation and plasma treatment. These results suggest that the Glidarc can be an effective solution for the reduction of sludge obtained during treatment by coagulation.

The gliding electric discharge in humid air is a source of activated species forming (e.g. (•)OH, (•)NO and their derivatives H2O2, ONO2H and NO3H) which are present in a non-thermal plasma at atmospheric pressure. These species are able to degrade organic pollutants in palm oil refinery wastewaters (PORW). The increase in acidity (pH decrease), conductivity and total dissolved solids (TDS) and the decrease in the total organic carbon (TOC) of PORW samples exposed to the discharge are reported. More than 50% TOC abatement is obtained for 15 min treatment in batch conditions with a laboratory reactor. The organic pollutants of PORW, i.e. mainly fatty acids are degraded according to a pseudo first-order reaction (k* = 0.06 min(-1)). Post discharge reactions are also observed after having switched off the discharge, which suggests that the pseudo first-order (k ≈ 0.05 min(-1)) degradation reactions should be attributed to the diffusion of soluble reactive species, e.g. H2O2 and ONOOH in the liquid target.

Mango seed, an abundant residue of the food industry, was used in its natural form (MS) and protonated form (AMS) as a biosorbent for the removal of Victazol Orange 3R (VO-3R) dye from its aqueous solutions. These biosorbents were characterized by infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and by nitrogen adsorption/desorption curves. Optimization of the effects of the initial pH of the dye solution, biosorbent dosage and contact time between the dye and the biosorbents on the biosorption capacities of the biosorbents was studied. Based on an error function ( F error ), the general order kinetic model provided the best fit to the experimental data when compared to the pseudo-first order and pseudo-second order kinetic biosorption models. The equilibrium data were fitted to Langmuir, Freundlich and Liu isotherm models. For both biosorbents, the equilibrium data were best fitted to the Liu isotherm model. Finally, the mechanism of biosorption involving VO-3R and lignin–cellulose was evaluated using the hybrid quantum mechanical/molecular mechanical (QM/MM) approach and molecular dynamic (MD) simulations. The results suggest that water molecules play a key role in the biosorption process.

Dilute solutions of organometallic complexes, i.e., Ferrocene and tris(1,10-phenanthroline)FeII or ferroin, readily oxidize when exposed to the gaseous species generated in a gliding electric discharge in humid air. Ferrocene (or bis-cyclopentadienyl FeII) turns to blue ferricinium ion while ferroin solutions fade. Ferroin is gradually oxidized to ferriin which agrees with the higher sensitivity of the central metal to the action of plasma than the organic ligand engaged in the complex. The oxidation hardly obeys a pseudo 1st order kinetics law (k 1 ∗ = 4 × 10−2 min−1). Additionally the oxidation reaction keeps on developing in post-discharge conditions according to a pseudo 1st order reaction (k 1 = 5 × 10−3 min−1). This feature tends to generalize the occurrence of temporal post-discharge reactions which are of major interest for industrial applications.

Dithizone is an extracting agent largely used for metallurgical processes and has been found in waste waters. Its degradation is studied by exposing basic solutions to a gliding arc discharge burning in various gases (i.e., humid and dry air, humid air and tert-butanol) to underline the role of the formed °OH radicals and H