Effect of non-oxidative plasma treatments on the surface properties of poly(p-phenylene terephthalamide) (PPTA) and poly(p-phenylene benzobisoxazole) (PBO) fibres as measured by inverse gas chromatography.

It has been shown in previous works that the interfacial adhesion in PPTA- and PBO-epoxy composites can be improved by modifying the surface properties of these high-performance fibres upon exposure to non-oxidative plasma treatments. In this work, the effects developed on both types of polymer surface were examined as a function of treatment gas nature (He or N2) and exposure time (one or four minutes) using inverse gas chromatography at infinite dilution (IGC). From the adsorption of n-alkanes, it has been proved that non-oxidative plasma treatments led to energetically heterogeneous surfaces in the case of PPTA, and to low-energy surfaces in the case of PBO. Nevertheless, it was proved with the 1-min plasma treatments (either under helium or under nitrogen) that chemical reactivity was enhanced on the PBO surface. Such a behaviour was ascribed to the presence of low-molecular weight oxidized materials. The mechanisms involved in surface activation of PPTA were not equivalent under He or N2 exposure. Nitrogen plasma exposure led to a PPTA surface that is chemically reactive as a result of polarity enhancement. Helium plasma-treated PPTA surface was characterized by the presence of branched arrangements that intensified the number of chemical contacts onto reactive sites. Finally, for both fibre sets, if the purpose is to enhance the chemical surface reactivity, it makes no sense to increase the plasma exposure time from 1 to 4 min.

Microwave-induced cracking of pyrolytic tars coupled to microwave pyrolysis for syngas production.

Herein a new process is proposed to produce a syngas-rich gas fraction (>80vol% H2+CO) from biowaste based on microwave heating within two differentiated steps in order to avoid tars production. The first step consists of the microwave pyrolysis of biowaste induced by a char-based susceptor at 400-800°C; tars, char and syngas-rich gas fractions being produced. The tars are then fed into the second step where a portion of the char from the first step is used as a bed material in a 0.3:1wt% ratio. This bed is heated up by microwaves up to 800°C, allowing thermal cracking of tars and additional syngas (>90vol% H2+CO) being then produced. This new concept arises as an alternative technology to the gasification of biowastes for producing syngas with no need for catalysts or gasifying reagents to minimise tars production.

Synergic adsorption in the simultaneous removal of acid blue 25 and heavy metals from water using a Ca(PO3)2-modified carbon.

We report the simultaneous adsorption of acid blue 25 dye (AB25) and heavy metals (Zn(2+), Ni(2+) and Cd(2+)) on a low-cost activated carbon, whose adsorption properties have been improved via a surface chemistry modification using a calcium solution extracted from egg shell wastes. Specifically, we have studied the removal performance of this adsorbent using the binary aqueous systems: AB25-Cd(2+), AB25-Ni(2+) and AB25-Zn(2+). Multi-component kinetic and equilibrium experiments have been performed and used to identify and characterize the synergic adsorption in the simultaneous removal of these pollutants. Our results show that the presence of AB25 significantly favors the removal of heavy metals and may increase the adsorption capacities up to six times with respect to the results obtained using the mono-cationic metallic systems, while the adsorption capacities of AB25 are not affected by the presence of metallic ions. It appears that this anionic dye favors the electrostatic interactions with heavy metals or may create new specific sites for adsorption process. In particular, heavy metals may interact with the -SO(3)(-) group of AB25 and to the hydroxyl and phosphoric groups of this adsorbent. A response surface methodology model has been successfully used for fitting multi-component adsorption data.

Surface modification of high-performance polymeric fibers by an oxygen plasma. A comparative study of poly(p-phenylene terephthalamide) and poly(p-phenylene benzobisoxazole).

Poly(p-phenylene terephthalamide) (PPTA) and poly(p-phenylene benzobisoxazole) (PBO) fibers were exposed to an oxygen plasma under equivalent conditions. The resulting changes in the surface properties of PPTA and PBO were comparatively investigated using inverse gas chromatography (IGC) and atomic force microscopy (AFM). Both non-polar (n-alkanes) and polar probes of different acid-base characteristics were used in IGC adsorption experiments. Following plasma exposure, size-exclusion phenomena, probably associated to the formation of pores (nanoroughness), were detected with the largest n-alkanes (C(9) and C(10)). From the adsorption of polar probes, an increase in the number or strength of the acidic and basic sites present at the fiber surfaces following plasma treatment was detected. The effects of the oxygen plasma treatments were similar for PPTA and PBO. In both cases, oxygen plasma introduces polar groups onto the surfaces, involving an increase in the degree of surface nanoroughness. AFM measurements evidenced substantial changes in the surface morphology at the nanometer scale, especially after plasma exposure for a long time. For the PBO fibers, the outermost layer - contaminant substances - was removed thanks to the plasma treatment, which indicates that this agent had a surface cleaning effect.

Removal of odour-causing compounds using carbonaceous adsorbents/catalysts prepared from sewage sludge.

This paper discusses H(2)S, NH(3) and VOCs removal by sewage-sludge-derived materials with outstanding chemical and textural properties. These materials were obtained from different precursors using different chemical and thermal treatments. Results show that the H(2)S removal process entailed a catalytic conversion of H(2)S to S or SO(4) (2-) species. On the other hand, adsorption is the main mechanism governing the performance of sludge-based materials for NH(3) and VOCs. Retention capacities (x/M values) obtained for some of the sludge-based adsorbents/catalysts are similar to those obtained with commercial activated carbons selected as reference materials.

High surface area materials prepared from sewage sludge-based precursors.

This paper focuses on physical activation (CO2) and chemical activation (H3PO4, NaOH and KOH) of sewage sludge-based precursors. Our results show that (i) a simple acid washing treatment leads to a significant increase in the adsorption capacity of some precursors; (ii) under the experimental conditions tested, CO2 physical activation and chemical activation with H3PO4 were ineffective for an efficient porosity development and (iii) choosing an appropriate protocol, it is possible to obtain highly porous materials (700-1700 m2 g(-1)) by chemical activation of sludge-based precursors with alkaline hydroxides. The efficiency of the chemical activation with NaOH or KOH is very much influenced by the method used for mixing the activating agent and the precursor. The BET values of the materials obtained when physically mixing ground hydroxides with the precursor almost doubled the values obtained if other mixing methods are employed. Increasing the hydroxide:precursor ratio leads to an enhancement of the adsorption capacity of the adsorbents, with BET values ranging from 689 to 1224 m2 g(-1) for NaOH activation and from 853 to 1686 m2 g(-1) for KOH activation.