Removal of diclofenac from aqueous solutions by adsorption on thermo‑plasma expanded graphite

The adsorption of diclofenac on thermo-plasma expanded graphite (a commercial product) from water solutions was investigated. The adsorbent material was characterized by SEM, TEM, BET, Raman and X-ray diffraction analyses. Typical diffractogram and Raman spectrum of graphitic material, dimension of 24.02 nm as crystallite dimension and a surface area of 47 m2 g−1 were obtained. The effect of pH on the adsorption capacity was evaluated in the range 1–7 and the adsorption mechanism was described by kinetic and isothermal studies. Pseudo-second order and Dubinin–Radushkevich models agreed with theoretical values of adsorption capacity (i.e. 400 and 433 mg g−1, respectively) and resulted to be the best fit for kinetics and isothermal experimental data. The thermodynamics of the process was evaluated by plotting the adsorption capacity/concentration ratio at the equilibrium as a function of different values of the multiplicative inverse of temperature. Moreover, the adsorbent regeneration was also investigated, comparing two different remediation techniques. Solvent washing performed with NaOH 0.2 M and thermo-treatment carried out by heating in an oven at 105 °C for 2 h and then at 200 °C for 4 h. The thermo-treatment was the best technique to regenerate the adsorbent, ensuring same performance after 4 cycles of use and regeneration

“Development and characterization of innovative adsorbent materials for the remediation of contaminated water”

The present thesis deeply investigated the use of a commercial innovative material, the thermoplasma-expanded graphite (TPEG), as adsorbent material for water remediation. This innovative material has never been used for this kind of applications and this thesis would demonstrate its effective use for water and groudwater remediation. TPEG is a promising material for that purpose due to its characteristics, evidenced by the producer, such as: high surface area and very significative expansion of interlayer distance of the plan of graphite. The commercial form of the TPEG is a very light powder that floats on the water, therefore, it was used in its natural form in batch tests. Adsorption of different pollutants, such as methylene blue, thricloethylene and diclofenac, was deeply investigated by evaluating the kinetics and isothermal aspect of the adsorption. Furthermore, other parameters that can affect the adsorption, such as pH, initial concentration of pollutants, ionic strength or presence of interference, were investigated. The possibility of regenerating and reusing the TPEG as adsorbent was also evaluated. Modification of the morphology of TPEG was conducted in order to use it as adsorbent material for different setup of process, like fixed-bed column. To this aim, the commercial form was transformed into a granular form of thermo-plasma expanded graphite (GTPEG), by entrapping TPEG into calcium alginate, by using a process that was developed and optimized during tihis thesis work. The GTPEG was then used to treat water by adsorption on fixed bed column. The process was deeply investigated and several pollutants were tested as target compounds, such as short chain phthalates (plasticizers), carbamazepine, bisphenol, 1,7-α ethynilestradiol and atrazine. The effect of adsorbent dosage, flow rate, initial concentration of pollutants, time contact and composition of GTPEG was evaluated. Other tests were conducted to verify the leaching of GTPEG. Adams-Bohart and Thomas models can effective applied to modelize the process and to evaluate its scale up. A sonication process was optimised to transform the not soluble TPEG into a hydrosoluble form, useful to treat groundwater by injecting the adsorbent material to obtain a hydraulic barrier able to contain and remove the pollution. By using this hydrosoluble form, TPEG can be used as material for the installation of injectable permeable reactive barrier. The capacity of the hydrosoluble TPEG to adsorb BTEX was firstly tested and characterized by using the batch setup to have all the information on the adsorption process. After the deeply characterization of the adsorption process, the use as injectable permeable reactive barrier to remove BTEX from groundwater was investigated. Innovative commercial materials can be used as adsorbent, but waste materials also represent a source of adsorbent materials. For this reason, a little part of the thesis was reserved to this kind of work. The last chapter reports a study conducted on the reuse of agricultural-food waste as adsorbent material: the spent ground coffee. The ability of spent ground coffee as adsorbent material was demonstrated by deeply investigating its capability to remove methylene blue

Removal of organic micropollutants from water by adsorption on thermo‑plasma expanded graphite encapsulated into calcium alginate

Nowadays, public concern is focused on the degradation of water quality. For this reason, the development of innovative technologies for water treatment in view of (micro)pollutant removal is important. Indeed, organic (micro)pollutants, such as pharmaceuticals, herbicides, pesticides and plasticizers at concentration levels of μg L−1 or even ng L− 1 are hardly removed during conventional wastewater treatment. In view of this, thermo-plasma expanded graphite, a light-weight innovative material in the form of a powder, was encapsulated into calcium alginate to obtain a granular form useful as filtration and adsorption material for removal of different pollutants. The produced material was used to remove atrazine, bisphenol-A, 17-α-ethinylestradiol and carbamazepine (at concentration levels of 125, 250 and 500 μg L−1) by top-down filtration. The effect of flow rate, bed depth and adsorbent composition was evaluated based on breakthrough curves. The experimental data was analysed with the Adams-Bohart model in view of scale-up. Under optimal conditions, removal and adsorption capacity of respectively about 21%, 21%, 38%,42%, 43 μg g−1, 44 μg g−1, 37 μg g−1 and 87 μg g−1 were obtained for atrazine, bisphenol, 17-α ethinylestradiol and carbamazepine when using 0.12 g of thermo-plasma expanded graphite to treat 200 mL at 500 μg L−1 (for each compound) of solution obtaining at contact time of 20 min. The granular form of TPEG obtained (GTPEG) by entrapping in calcium alginate results to have a good adsorbent property for the removal of carbamazepine, atrazine, bisphenol A and 17-α ethinylestradiol from water at concentration levels between 250 and 500 μg L− 1. Promising results confirm the adsorbent properties of TPEG and push-up us to investigate on its application and improve of its performance by evaluating different entrapping materials

Mussel-Inspired Electro-Cross-Linking of Enzymes for the Development of Biosensors

International audienceIn medical diagnosis and environmental monitoring, enzymatic biosensors are widely applied because of their high sensitivity, potential selectivity, and their possibility of miniaturization/automation. Enzyme immobilization is a critical process in the development of this type of biosensors with the necessity to avoid the denaturation of the enzymes and ensuring their accessibility toward the analyte. Electrodeposition of macromolecules is increasingly considered to be the most suitable method for the design of biosensors. Being simple and attractive, it finely controls the immobilization of enzymes on electrode surfaces, usually by entrapment or adsorption, using an electrical stimulus. Performed manually, enzyme immobilization by cross-linking prevents enzyme leaching and was never done using an electrochemical stimulus. In this work, we present a mussel-inspired electro-cross-linking process using glucose oxidase (GOX) and a homobifunctionalized catechol ethylene oxide spacer as a cross-linker in the presence of ferrocene methanol (FC) acting as a mediator of the buildup. Performed in one pot, the process takes place in three steps: (i) electro-oxidation of FC, by the application of cyclic voltammetry, creating a gradient of ferrocenium (FC+); (ii) oxidation of bis-catechol into a bis-quinone molecule by reaction with the electrogenerated FC+; and (iii) a chemical reaction of bis-quinone with free amino moieties of GOX through Michael addition and a Schiff's base condensation reaction. Employed for the design of a second-generation glucose biosensor using ferrocene methanol (FC) as a mediator, this new enzyme immobilization process presents several advantages. The cross-linked enzymatic film (i) is obtained in a one-pot process with nonmodified GOX, (ii) is strongly linked to the metallic electrode surface thanks to catechol moieties, and (iii) presents no leakage issues. The developed GOX/bis-catechol film shows a good response to glucose with a quite wide linear range from 1.0 to 12.5 mM as well as a good sensitivity (0.66 μA/mM cm2) and a high selectivity to glucose. These films would distinguish between healthy (3.8 and 6.5 mM) and hyperglycemic subjects (>7 mM). Finally, we show that this electro-cross-linking process allows the development of miniaturized biosensors through the functionalization of a single electrode out of a microelectrode array. Elegant and versatile, this electro-cross-linking process can also be used for the development of enzymatic biofuel cells

Mussel-Inspired Electro-Cross-Linking of Enzymes for the Development of Biosensors

In medical diagnosis and environmental monitoring, enzymatic biosensors are widely applied because of their high sensitivity, potential selectivity, and their possibility of miniaturization/automation. Enzyme immobilization is a critical process in the development of this type of biosensors with the necessity to avoid the denaturation of the enzymes and ensuring their accessibility toward the analyte. Electrodeposition of macromolecules is increasingly considered to be the most suitable method for the design of biosensors. Being simple and attractive, it finely controls the immobilization of enzymes on electrode surfaces, usually by entrapment or adsorption, using an electrical stimulus. Performed manually, enzyme immobilization by cross-linking prevents enzyme leaching and was never done using an electrochemical stimulus. In this work, we present a mussel-inspired electro-cross-linking process using glucose oxidase (GOX) and a homobifunctionalized catechol ethylene oxide spacer as a cross-linker in the presence of ferrocene methanol (FC) acting as a mediator of the buildup. Performed in one pot, the process takes place in three steps: (i) electro-oxidation of FC, by the application of cyclic voltammetry, creating a gradient of ferrocenium (FC⁺); (ii) oxidation of bis-catechol into a bis-quinone molecule by reaction with the electrogenerated FC⁺; and (iii) a chemical reaction of bis-quinone with free amino moieties of GOX through Michael addition and a Schiff’s base condensation reaction. Employed for the design of a second-generation glucose biosensor using ferrocene methanol (FC) as a mediator, this new enzyme immobilization process presents several advantages. The cross-linked enzymatic film (i) is obtained in a one-pot process with nonmodified GOX, (ii) is strongly linked to the metallic electrode surface thanks to catechol moieties, and (iii) presents no leakage issues. The developed GOX/bis-catechol film shows a good response to glucose with a quite wide linear range from 1.0 to 12.5 mM as well as a good sensitivity (0.66 μA/mM cm²) and a high selectivity to glucose. These films would distinguish between healthy (3.8 and 6.5 mM) and hyperglycemic subjects (>7 mM). Finally, we show that this electro-cross-linking process allows the development of miniaturized biosensors through the functionalization of a single electrode out of a microelectrode array. Elegant and versatile, this electro-cross-linking process can also be used for the development of enzymatic biofuel cells