Rice straw (RS), rice husk (RH) and polyethylene (PE) were blended and submitted to gasification and pyrolysis processes. The chars obtained were submitted to textural, chemical, and ecotoxic characterisations, towards their possible valorisation. Gasification chars were mainly composed of ashes (73.4–89.8wt%), while pyrolysis chars were mainly composed of carbon (53.0–57.6wt%). Silicon (Si) was the major mineral element in all chars followed by alkaline and alkaline-earth metal species (AAEMs). In the pyrolysis chars, titanium (Ti) was also a major element, as the feedstock blends contained high fractions of PE which was the main source of Ti. Gasification chars showed higher surface areas (26.9–62.9m2g−1) and some microporosity, attributed to porous silica. On the contrary, pyrolysis chars did not present a porous matrix, mainly due to their high volatile matter content. The gasification bed char produced with 100% RH, at 850°C, with O2 as gasification agent, was selected for further characterization. This char presented the higher potential to be valorised as adsorbent material (higher surface area, higher content of metal cations with exchangeable capacity, and lowest concentrations of toxic heavy metals). The char was submitted to an aqueous leaching test to assess the mobility of chemical species and the ecotoxic level for V. fischeri. It was observed that metallic elements were significantly retained in the char, which was attributed mainly to its alkaline character. This alkaline condition promoted some ecotoxicity level on the char eluate that was eliminated after the pH correction.

The aim of the present work was to assess the efficiency of biochars obtained from the co-gasification of blends of rice huskþinspace}+þinspace}corn cob (biochar 50CC) and rice huskþinspace}+þinspace}eucalyptus stumps (biochar 50ES), as potential renewable low-cost adsorbents for Cr(III) recovery from wastewaters. The two gasification biochars presented a weak porous structure (ABETþinspace}=þinspace}63–144 m2 g−1), but a strong alkaline character, promoted by a high content of mineral matter (59.8{%} w/w of ashes for 50CC biochar and 81.9{%} w/w for 50ES biochar). The biochars were used for Cr(III) recovery from synthetic solutions by varying the initial pH value (3, 4, and 5), liquid/solid (L/S) ratio (100–500 mL g−1), contact time (1–120 h), and initial Cr(III) concentration (10–150 mg L−1). High Cr(III) removal percentages (around 100{%}) were obtained for both biochars, due to Cr precipitation, at low L/S ratios (100 and 200 mL g−1), for the initial pH 5 and initial Cr concentration of 50 mg L−1. Under the experimental conditions in which other removal mechanisms rather than precipitation occurred, a higher removal percentage (49.9{%}) and the highest uptake capacity (6.87 mg g−1) were registered for 50CC biochar. In the equilibrium, 50ES biochar presented a Cr(III) removal percentage of 27{%} with a maximum uptake capacity of 2.58 mg g−1. The better performance on Cr(III) recovery for the biochar 50CC was attributed to its better textural properties, as well as its higher cation exchange capacity.

The adsorption of four phenolic compounds (gallic acid, protocatechuic acid, vanillic acid and syringic acid) is investigated using a synthesized mesoporous carbon on both single and multi-component synthetic solutions. Some correlation of the adsorption capacity of the carbon and the nature of adsorbate could be made, except for gallic acid whose concentration decrease seems to be not exclusively due to adsorption but also to polymerization reaction. In the multi-component mixture, negative effects in the adsorption capacity are observed probably due to competition for the active centers of the adsorbent surface. In desorption studies, ethanol presents better performance than water and acetonitrile. Vanillic acid is the compound with the higher adsorption and interestingly it is then possible to desorb a relatively high amount of it from the adsorbent, which may represent a possibility for a selective recovery of vanillic acid. These results present a potential way to treat the wastewater from the cork industry.

This work is dedicated to study the potential application of char byproducts obtained in the gasification of rice husk (RG char) and rice husk blended with corn cob (RCG char) as removal agents of two emergent aquatic contaminants: tetracycline and caffeine. The chars presented high ash contents (59.5–81.5{%}), being their mineral content mainly composed of silicon (as silica) and potassium. The samples presented a strong basic character, which was related to its higher mineral oxides content. RCG char presented better textural properties with a higher apparent surface area (144 m2 g−1) and higher micropore content (V micro = 0.05 cm3 g−1). The alkaline character of both chars promoted high ecotoxicity levels on their aqueous eluates; however, the ecotoxic behaviour was eliminated after pH correction. Adsorption experiments showed that RG char presented higher uptake capacity for both tetracycline (12.9 mg g−1) and caffeine (8.0 mg g−1), indicating that textural properties did not play a major role in the adsorption process. For tetracycline, the underlying adsorption mechanism was complexation or ion exchange reactions with the mineral elements of chars. The higher affinity of RG char to caffeine was associated with the higher alkaline character presented by this char.

Adsorption of model systems of triclosan by mineral sorbent diatomite is studied. The triclosan equilibrium concentration was measured spectrophotometrically, the morphology of the diatomite characterized using scanning electron microscopy and the amount of the adsorbed triclosan on the diatomite quantified by a mass balance. Adsorption isotherms were analyzed according to the linear/nonlinear form of Langmuir, Freundlich, Sips and Toth isotherm models isotherms, using AMPL software. It is shown that nonlinear Langmuir and Sips isotherm model provided suitable fitting results and no pronounced difference in adsorption efficiency between isotherms measured after 1, 2 and 3days adsorption was observed. Determined maximum adsorption capacity of diatomite towards triclosan qs is 140mg/g. Averaged calculated values of ΔG are −9.9 and −9.6kJ/mol for Langmuir and Sips models respectively. The negative sign of such values indicates spontaneous, physical in nature adsorption.

The adsorption of triclosan as model system was studied to qualify activated carbon sorbents recycled from gas masks (civilian gas mask GP5). The triclosan equilibrium concentration was measured spectrophotometrically, the morphology of the activated carbon characterized by scanning electron microscopy, and the amount of the adsorbed triclosan on the activated carbon quantified by a mass balance method. Experimental isotherms were fitted by Langmuir, Freundlich and Sips adsorption models. It was obtained that the contact time is a crucial sorption parameter that provides information on the optimum adsorption efficiency. It was shown that the maximum efficiency of GP5 (88%) is obtained after 10days of adsorption at a maximal concentration of triclosan and carbon loading 1mg/l. No significant adsorption efficiency differences were measured after 5 and 10days of adsorption. The non-linear Sips isotherm, a combined Freundlich–Langmuir model, provides suitable fitting results. The observed remarkable adsorption capacity of activated carbon (GP5) towards triclosan adsorption (∼85mg/g) makes it a viable solution for wastewater treatment.

The thermoelectric (TE) properties of vanadium pentoxide (V2O5) alloyed with graphite (G) were studied as a function of its incorporation percentage. Variable weight percentages of graphite powder (0–50{%}) were added to V2O5 powder and their mixtures were evaporated by a thermal evaporation technique to form thin films with a thickness in the range of 30–80 nm. In the infrared wavelength region, the transmittance of the obtained films increased as the G percentage was increased, while in the visible range, it decreased with G up to 10{%}. The TE properties were improved when G was in the range of 10–30{%}, while it decreased for the other percentages: Seebeck coefficient (S) changed from 0.6 mV/K to 0.9 mV/K and was zero with a G of 50{%}; the electrical conductivity varied slightly from 5 ($Ømega$m)−1 to 0.7 ($Ømega$m)−1 while the mobility improved from 0.07 cm2/V s to 1.5 cm2/V s and the respective carrier concentration was reduced, from 1 × 1018 cm−3 to 4 × 1016 cm−3. These films were applied as temperature sensors evaluating the thermovoltage as a function of thermal gradient between two electrodes, in which one was maintained at room temperature.