Ignazio Renato Bellobono

Laboratory- and pilot-plant-scale photodegradation of chloroaliphatics in aqueous solution by photocatalytic membranes immobilizing titanium dioxide☆

The TiO2-medicated photodegradation of chloroaliphatics (dichloromethane, trichloroethene and mono-, di- and trichloroethanoic acids) was studied at 308±2 K (with the ratio between the hydrogen peroxide added and the stoichiometric amount (N) in the range 0–30), using PHOTOPERMTMCPP/313 membranes containing immobilized 30%±3% TiO2, at laboratory scale (radiant power in the absorption range, 145 W) and in a pilot plant (radiant power in the absorption range, 31 W). In addition to this semiconductor, some proprietary photocatalytic systems, including stabilized preparations containing CoIII, VV and FeIII organometallic compounds, were immobilized in the photocatalytic membranes. The initial rate of photodegradation was studied as a function of the initial concentration of the substrates (5.0×10-2–5.0×10-7M) using the linearized form of the Langmuir-Hinshelwood equation, which was well fitted by the membranes over the whole range of concentration, and from which the rate constants k and equilibrium adsorption constants K were evaluated. The contributions of processes (a)-(d) ((a) photolysis of micropollutant, independent of the presence of membranes and oxidizing agent; (b) photo- degradation due to UV and hydrogen peroxide; (c) photodegradation due to the semiconductor immobilized in the membrane; (d) the same as (c), but in the presence of a promoting photocatalytic system), which occur simultaneously in our experimental conditions, were measured. The contribution of process (d), particularly for a synergistic mixture of tri-(tert-butyl) and tri-(isopropyl) vanadate(V) or iron (III) potassium oxalate as photocatalysts, is greater than that of all other processes, while UV degradation in the presence of hydrogen peroxide (b) represents one-tenth or less of the whole. The rationalization of k values for this integrated membrane process is discussed on the basis of their dependence on the membrane surface and on the square root of the radiation intensity.

Laboratory-scale photodegradation of phenol in aqueous solution by photocatalytic membranes immobilizing titanium dioxides☆

The TiO2-mediated photodegradation of phenol was studied at 298 ± 2 or 308 ± 2 K (with the ratio between the hydrogen peroxide added and the stoichiometric amount (N) in the range 0–10), using PHOTOPERM® CPPI313 membranes containing immobilized 30 ± 3 wt.% TiO 2, with high or low pressure mercury arc lamps (radiant power in the absorption range, 145 and 8 W respectively). The initial rate of photodegradation was studied as a function of the initial concentration of substrate (1.0x10−5−0.12 M) using the linearized form of the Langmuir-Hinshelwood equation, from which the rate constants k and apparent equilibrium adsorption constants K were evaluated. The rationalization of k and K values on the basis of their dependency on N, the apparent reaction order, the advantages of the membrane process with respect to the use of colloidal suspensions of TiO2, also tested in comparable conditions, and the kinetic significance of K, on the basis of no measurable dark adsorption onto the photocatalytic membranes, are discussed.

Surface Interactions of Actinides with Alumina Colloids

Results are given on the influence of pH, carbonates and humic substances on the adsorption of Am (III), Th(IV) and Np(V) onto alumina colloids at fixed ionic strength. Surface interactions are oxidation state dependent, with adsorption edges shifting toward high pH in the order Th(IV), Am (III), Np(V). Carbonate ions markedly reduce the adsorption of neptunium, americium and thorium at relatively high pH. The addition of humic substances increases the actinide uptake at low pH and lowers the adsorption by the colloidal particles in the neutral to alkaline pH range.

Mathematical modelling of photomineralization of phenols in aqueous solution, by photocatalytic membranes immobilizing titanium dioxide☆

Photomineralization of phenol, 2,6-dimethyl phenol, 1,2,3-benzenetriol, 4-chloro phenol, and 2,4-dichloro phenol, in 9.9×10−3 − 5.6×10−5 M aqueous solutions, in the presence of stoichiometric hydrogen peroxide, was studied, using PHOTOPERM® CPP/313 membranes containing immobilized 30±3 wt.% TiO2, by analysis of total organic carbon (TOC) content. With phenol and 2,6-dimethyl phenol also the rate of disappearance of the substrate molecules was measured fluorimetrically. Polychromatic or monochromatic irradiation was carried out (radiant power in the absorption range 145 and 8 W respectively). The initial rate of photodegradation was studied as a function of the initial concentration of substrate using the linearized form of the Langmuir-Hinshelwood equation, from which the rate constants k and apparent adsorption constants K were evaluated. These parameters, which are unable to fit the whole photomineralization kinetic curves, were employed to optimize, by numerical integration, a kinetic model which considers appearance and disappearance of all intermediates, as if they were represented by a hypothetical single molecule, mediating all of them. By this way, two couples of parameters, k1 and K1, k2 and K2 were obtained, relative to the two successive steps of the model (substrate disappearance and mineralization), able to reproduce satisfactorily well the whole kinetics. Experimental data, as compared to modelling, show evidence of a main rate determining path, and of another, minor but not unsignificant, parallel path leading to a faster mineralization. Mean quantum yields of organic carbon mineralization, calculated by k2 parameters, reach 10–20% of the maximum allowable efficiencies.

Photosynthetic membranes. VI. Characterization of ultrafiltration membranes prepared by photografting zeolite-epoxy-diacrylate resin composites onto cellulose☆

Water permeability measurements were carried out at 20°C through membranes prepared by photochemically grafting an epoxy-diacrylate copolymer or one of its zeolite composites onto cellulose. A correlation between mean pore diameter and water flux per unit applied pressure drop has been established, the latter being in turn related to membrane thickness. In Poiseuilles laminary flow regime, with a normal Kozeny-Carman constant indicating a regular packing of isometrically shaped particles in the microporous medium, surface areas of zeolites 3A, 5A, and 13X could be evaluated as 628, 482, and 403 m2-g− respectively, while a value of 102 m2-g−1 resulted for the polymeric membrane. Rejection characteristics for poly(ethylene glycol) (PEG) polymers dissolved in water have been investigated. Linear relationships between water flux per unit applied pressure drop and molecular weight of PEG polymers at constant solute rejection have been obtained, independent of the kind of photosynthetic membrane, whether polymeric zeolite free or composite. Characterization of asymmetric membranes, prepared photochemically, by the methods used, gives consistent results as regards structural parameters and geometric configuration of these membranes.

Pilot-Plant-Scale Photodegradation of Phenol in Aqueous Solution by Photocatalytic Membranes Immobilizing Titanium Dioxide (Photoperm Process)

The TiO2-mediated photodegradation of phenol was studied at 298 ± 2 K or at 315 ± 5 K (with the ratio between the hydrogen peroxide added and the stoichiometric amount (N) in the range 0 – 3), using PHOTOPERM® CPP/313 membranes containing immobilized 30 ± 3 wt.% TiO 2. The rate of photodegradation was studied as a function of: i) initial concentration of substrate (8.76x10−6 − 0.01 M), ii) flow rate (0.4 – 5 m3/h),iii) apparent (geometrical) membrane surface (30 – 190 cm2/cm of central axis of radiation field), iv) kind of radiation source (low and high pressure mercury arc lamps, with fixed or variable radiant power, in the absorption range of semiconductor, of 31 W and 136–680 W respectively), v) radiation intensity. Disappearance of both phenol and total organic carbon (TOC) was examined. The operations of two pilot-plants, differing in range of flow rates, and membrane arrangement, are critically compared. The apparent reaction orders as a function of concentration are also compared and discussed, on the basis of kinetic parameters resulting from both pilot-plant- and laboratory-scale experience. Advantages of the membrane process are highlighted.

EPR spin-trapping of hydroxyl radicals onto photocatalytic membranes immobilizing titanium dioxide, and spin adduct competition, as a probe of reactivity with aqueous organic micropollutants

Abstract Spin-trapping of photogenerated •OH radicals, with electron paramagnetic resonance (EPR) detection of spin adducts, has been evidenced on to photocatalytic membranes, prepared by photografting, and immobilizing 30±3 wt.% TiO2 semiconductor. By employing the known rate constant for the reaction of •OH radicals with the spin-trap (DMPO), rate constants for the reaction of •OH radicals with a given substrate could be obtained by a competition kinetic scheme, using the initial rates of the first step of photodegradation of the substrate. This method used, for a parallel series of runs, also membranes, immobilizing 7 wt.% of trialkyl vanadates as photocatalytic promoters together with the semiconductor, able to yield unitary quantum yields for the photogeneration of •OH radicals from semiconductor. Quantum yields for the non-photocatalytically promoted semiconductor membrane could thus be obtained. This method has been validated with phenol, 4-chlorophenol, 2,4-dichlorophenol, atrazine, propazine, prometryn, ametryn, and formate ion, and compared with a similar technique, set up recently in the literature, based on production of •OH by homogeneous photolysis of H2O2 and direct EPR measurements of the rate of spin adduct formation.

Photooxidation of prometryn and prometon in aqueous solution by hydrogen peroxide on photocatalytic membranes immobilising titanium dioxide

Abstract The TiO 2 -mediated photooxidation of prometryn and prometron in aqueous solution by PHOTOPERM ® CPP/313 membranes containing immobilized 30±3 wt.% TiO 2 and by employing hydrogen peroxide was studied. This oxygen donor was used as a substitute of dissolved oxygen or ozone by which complete mineralization of s -triazines had been attained on photocatalytic membranes as reported previously. Solutions containing 5.2·10 −6 –1.0·10 −4 M prometryn and 7.8·10 −6 –2.0·10 −4 M prometon were photodegraded successfully. Experiments were carried out in a PHOTOPERM ® WP pilot-plant using monochromatic irradiation (254 nm) in the absorption range of semiconductor with an absorbed power of 11 ± 1 W. For the disappearance of both substrates, pseudo-first order kinetics were observed and the results could be interpreted by the Langmuir-Hinshelwood treatment. Cyanuric acid, however, resulted as final product under the experimental conditions. This behaviour is compared with that of the use of oxygen or ozone as oxygen donors. Furthermore, based on HPLC and HPIC analysis, a mechanism of photodegradation is proposed for both substrate molecules.

Photobleaching and photomineralization of azobenzene and substituted azobenzenes in aqueous solution by photocatalytic membranes immobilizing titanium dioxide

Abstract The kinetics of photobleaching (by spectrophotometric analysis) and integral photomineralization (by total organic carbon (TOC) analysis) of azobenzene ( I ) and substituted azobenzenes in aqueous solution were followed in laboratory-scale runs on photocatalytic membranes immobilizing 30±3 wt.% of semiconductor TiO 2 . Experiments were carried out by the technique described in preceding papers of this series, employing stoichiometric hydrogen peroxide as the oxygen donor. The following azobenzenes were examined: (4-diethylamino)-phenylazobenzene ( II ), 4′-(((4-diethylamino)phenyl)azo) benzoic acid ( III ), 4′-(((2-amino-5-diethylamino)phenyl)azo) benzoic acid ( IV ), 4′-(((2-acetamido-4-diethylamino)phenyl)azo) benzoic acid ( V ), 4′-(((4-dimethylamino)phenyl)azo) benzenesulphonic acid, sodium salt ( VI ) and 4′-(((2-acetamido-4-diethylamino)phenyl)azo) benzenesulphonic acid, sodium salt ( VII ). From the Langmuir-Hinshelwood treatment of the initial rate data as a function of the initial concentration ((0.10−1.0) × 10 −3 M), the kinetic parameter k and the pseudo-thermodynamic parameter K for photobleaching were obtained. With regard to photobleaching, I and II were certainly the most reactive, followed by IV . The remaining molecules showed a photo-oxidation rate of one-third to one-quarter of that of I chosen as reference structure. Consequently, the presence of an amino group in the 4-position ( II ) does not stabilize the azobenzene structure against photo-oxidation leading to bleaching, whereas the same group in the 2-position ( IV ) decreases the photobleaching rate by about 40% when a carboxylic group is also present in the I′-position. Acetylation of this amino group, such as in V , decreases the photobleaching rate more markedly. With regard to photomineralization, it was observed that, when photobleaching was virtually complete, a certain amount of TOC was already mineralized. The maximum amount of TOC remaining at the end of photobleaching ranged from about 90% to about 30%, varying with the dye structure and initial concentration as well as with the power and type of irradiation source. By examining the TOC concentration profiles as a function of the substituted azobenzene structure, the following hypotheses were proposed: 1. 1. during the photobleaching period, the ring containing the diethylamino group breaks down (more markedly if further amino or acetamido groups are present in the structure), and photomineralization of the other ring occurs more slowly: 2. 2. both rings break down, within certain limits, during photobleaching; however, the aliphatic fragments containing carboxyl or sulphonic groups are mineralized more slowly. The fact that a small initial plateau in the TOC profile is followed by another more evident plateau at the end of the photobleaching period, for both VI and VII , suggests that hypothesis (1) is more probable in these cases. When the second plateau is reduced to a sigmoidal curve or an inflection point, hypothesis (2) also needs to be considered.

Degradation of some chloro-aliphatic water contaminants by photocatalytic membranes immobilizing titanium dioxide☆

Abstract The TiO 2 -mediated photodegradation of chloroethanoic acid, trichloroethene and tetrachloroethene, chosen as model molecules of aliphatic chloro-organics was studied at 303±2 K by employing polymeric membranes photografted on cellulose to immobilize the TiO 2 (3.0–5.6 mg cm −2 ). The radiant flux in the absorption range and the volume-surface ratio in the photoreactor cell were kept constant at 2.5±0.2 mW cm −2 and 1.1±0.1 mL cm −2 respectively. The initial rate of photodegradation was studied as a function of the initial concentration of reactants by the linearized form of the Langmuir—Hinshelwood equation, by which rate constants k and equilibrium adsorption constants K were evaluated. Values of k (5.7±0.5 μmol h −1 ) are independent of the chemical nature of the three reactants investigated, in agreement with other literature findings. Values of K are compared with those measured in aqueous suspensions of TiO 2 with the same chloro-organics and with the values predicted by a mechanism involving hydroxyl radicals as the primary oxidant adsorbed on the photocatalyst surface. Satisfactory performance and potential technological advantages of photocatalytic membranes are discussed.