Biochar is becoming a low-cost substitute of activated carbon for the removal of multiple contaminants. In this study, five biochar samples derived from pine sawdust were produced at different pyrolysis temperatures (300 °C-700 °C) and used adsorbents to remove p-nitrophenol from water. Results indicate that, as the pyrolysis temperature increases, the surface structure of biochar grows in complexity, biochar's aromaticity and number of functional group decrease, and this material's polarity increases. Biochar's physiochemical characteristics and dosage, as well as solution's pH and environmental temperature significantly influence the p-nitrophenol adsorption behavior of biochar. p-nitrophenol adsorption onto biochar proved to be an endothermic and spontaneous process; furthermore, a greater energy exchange was observed to take place when biochar samples prepared at high temperatures were utilized. the adsorption mechanism includes physical adsorption and chemisorption, whereas its rate is mainly affected by intra-particle diffusion. Notably, in biochar samples prepared at low temperature, adsorption is mainly driven by electrostatic interactions, whereas, in their high-temperature counterparts, p-nitrophenol adsorption is driven also by hydrogen bonding and π-π interactions involving functional groups on the biochar surface.
A novel wideband down‐conversion mixer is proposed for multi‐standard wireless applications between 100 MHz and 2.5 GHz. A transconductance stage with two pairs of compensatory transistors is adopted for high linearity. Differing from the ordinary differential multi‐gated transistor technique utilised in Gilbert mixer, the design proposed concerns about both gm″ and gm compensation of the transconductance stage in order to improve both input‐referred third‐order intercept point (IIP3) and 1 dB gain compression point (CP1 dB). Realising in Taiwan Semiconductor Manufacturing Company (TSMC) 180 nm RF CMOS process, the mixer provides a gain of 8.9 dB, a maximum IIP3 of 5.8 dBm, a maximum CP1 dB of −4 dBm and a minimum noise figure (NF) of 9.6 dB.
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