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Activated carbon (AC) is one of the most promising active materials for high-performance supercapacitors (SCs) owing to its high specific surface area and theoretical specific capacity. In this study, oil palm empty fruit bunches (EFBs), which are agricultural residue, are employed as a precursor to produce AC using a series of cleaning, carbonization, and chemical activation processes. The as-produced AC has a specific surface area of 2774 m2/g, which is very high among AC produced from biomass materials. To enhance the performance of SCs, the AC is modified by nitrogen doping. The specific capacities of AC and nitrogen-doped AC are found to be 182 to 217 F/g, respectively, at a current density of 0.5 A/g in 6 M KOH aqueous electrolyte. We demonstrate that agricultural waste can be processed into AC with a high specific surface area for SC applications. [ABSTRACT FROM AUTHOR]

Photocatalysis is one of the most promising advanced oxidation processes due to the capability of solid catalyst to continuously produce oxidant species under light irradiation. The use of conventional UV lamps is high cost intensive, which undermines the possible implementation in developing countries. Visible light active photocatalysts can overcome these challenges and find a market opportunity for competitive technology implementation. This work proposes the synthesis of visible light active catalyst following a facile sol-gel synthesis that introduces CuSO4 as dopant in TiO2. Results present complete abatement of methylene blue in 120 min of treatment under 50 mW cm−2 of blue light (λ = 450 nm), while commercial P25 TiO2 presented null abatement under identical conditions. Synthesis parameters including dopant level and calcination temperature allowed defining optimum synthesis conditions based on material characteristics modification and catalytic activity enhancement. A doping level of 0.21 mol% CuSO4 was identified as optimum condition to enable visible light photocatalysis of doped TiO2 catalysts calcined at 300 °C. Finally, operational parameters were evaluated defining a wide range of pH operation under 3.0 g L−1 of catalyst dose to treat up to 20 g L−1 of highly recalcitrant phenothiazine dye. These optimum conditions allowed complete dye removal under visible light after 120 min of treatment. [ABSTRACT FROM AUTHOR]

Purpose: The bioavailability of potassium (K) depends on its speciation distribution in the soil. Different methods are commonly used to estimate K speciation including traditional single leaching (TSL) and sequential extraction process (SEP). However, K speciation is largely affected by soil pretreatment methods. The effects of both TSL and SEP soil pretreatment methods were evaluated. Materials and methods: The TSL method classifies K speciation content based on bioavailability, while the SEP classifies the metal speciation based on the effects of environmental conditions. These two methods, together with a modified sequential single leaching (SSL) scheme, were used to evaluate five types of soil including soil without potassium fertilization, soil with long-term K fertilization, alkaline soil, red soil, and forest soil. The soil samples were gathered randomly at depths varying up to 30 cm before being dried in air at room temperature. The samples were then ground and mixed before passing through a sieve (10 mesh or 100 mesh) in order to perform K speciation analysis via the modified SSL technique, the TSL method, and the four schemes of SEP. Results and discussion: Soil pretreatment influenced K speciation, with higher concentration in soil samples sieved through 100 mesh than through 10 mesh. In alkaline soil, potassium was observed to be associated with carbonate. For the various SEP schemes, K speciation was found to be greatest in the residual fraction, with only 3% observed in the carbonate, exchangeable, metal organic complex, or amorphous hydroxides of Fe or Mn. After following the first two steps of the SEP schemes, the available K was similar to that of the TSL method. Distribution of non-exchangeable K using the TSL method was comparable with the five combined SEP extraction steps which were all affected by environmental conditions. Conclusions: Pretreatment affected K speciation distribution and total amount of metal in the soil. The 100 mesh sieve was more effective in estimating K soil speciation. The SEP method was acceptable for estimating K speciation, with the Krishnamurti et al. (Analyst 120:659-665, 1995) scheme as a useful appraisal of K bioavailability. Combination analyses using both TSL and SEP methods are useful techniques to enable a better understanding of K speciation transformation in soil. [ABSTRACT FROM AUTHOR]