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We develop a method for bifunctional regulation on the surface micro-morphology and nitrogen-doping configuration of graphene-based nanosheets by annealing chitin and graphene oxide. Systematic studies reveal that annealing temperature is a key to determine micro-morphology and type of nitrogen-doping of the graphene matrix, and 2D multi-wrinkled graphene (CS-rGO-600) with enriched active nitrogen species and moderate defects can be obtained successfully under an optimized annealing temperature. When used as a "green" electrocatalyst for oxygen reduction reaction (ORR), CS-rGO-600 exhibits superior performance, in terms of more outstanding electrode activity and durability, higher output power density in fuel cell system compared to that of Pt/C. These could be attributed to the fact that appropriate annealing treatment is not only conducive to exogenous nitrogen enrichment and oriented conversion but also beneficial to micro-structure construction. The synergistic effects between multi-wrinkled 2D structure and active sites endow CS-rGO-600 with superior ORR performance in the fuel cell. • CS-rGO-X was prepared via pyrolysis of biomass waste and GO. • Appropriate pyrolysis is conducive to N enrichment and structure construction. • Synergism between structure and active sites endow CS-rGO-600 with superior activity. • CS-rGO-600 with highest E onset (0.059 V) and P max (0.665 mWcm−2). [ABSTRACT FROM AUTHOR]

• The migration characteristics of heavy metals during sludge pyrolysis were studied. • The activation energy of sludge pyrolysis was determined by the Model-free method. • As the pyrolysis temperature increased, the concentration of CO decreased and then increased. • Cu, Cr, and Ni were seldom involved in migration during pyrolysis. • As, Cd, and Hg readily migrated even at low pyrolysis temperatures. A comprehensive study was conducted to investigate the pyrolysis characteristics of municipal sludge, and the activation energy of sludge pyrolysis was determined using the Model-free method. The detailed migration characteristics of heavy metals in the pyrolysis products were also investigated at different pyrolysis temperatures (250–850 °C). The results demonstrate that sludge pyrolysis is a multi-step process; the activation energy of pyrolysis increased with the pyrolysis conversion rate, and the average activation energy was calculated as 79.59 kJ mol−1. As the pyrolysis temperature increased, the char yield decreased, the tar yield increased then decreased, and the gas yield increased. At 850 °C, the thermal volatilities of heavy metals followed the sequence Cu < Cr < Ni < Mn < Pb < As < Zn < Cd = Hg. In addition, Cu, Cr, and Ni were seldom involved in migration during pyrolysis while As, Cd, and Hg readily migrated even at low pyrolysis temperatures. The results provide a theoretical basis for sludge pyrolysis technologies and heavy metals migration control. [ABSTRACT FROM AUTHOR]

A comprehensive study was conducted to assess the characteristics of basic oxygen furnace slag (BOFS) and electric arc furnace slag (EAFS) as oxygen carriers for chemical looping gasification (CLG) of sewage sludge (SS). The surface roughness and wear resistance of BOFS were found to be higher than those of EAFS. Further, the oxygen transport capacity of BOFS was higher than that of EAFS at 800 ° C and 900 ° C with the same redox cycles. As the mass ratio increased, the carbon conversion rate and CO 2 concentration gradually increased, while the water conversion rate, cold gas efficiency, and H 2 and CO concentrations initially increased and then decreased. Both BOFS and EAFS as oxygen carriers had the highest carbon conversion rate and cold gas efficiency when the steam flow rate was 0.15 g min−1. The cyclic reactivity of BOFS as an oxygen carrier in the CLG process decreased faster than that of EAFS. However, the content of combustible components of BOFS as an oxygen carrier was significantly higher than that of EAFS in each cycle. Overall, these results provide a theoretical basis for steel slag as an oxygen carrier for the CLG of SS. • Steel slag was used as oxygen carrier for chemical looping gasification of sludge. • Basic oxygen furnace slag and electric arc furnace slag were selected for study. • Basic oxygen furnace slag has higher surface roughness and wear resistance. • Basic oxygen furnace slag as oxygen carrier produced more combustible components. • Basic oxygen furnace slag is more suitable as oxygen carrier. [ABSTRACT FROM AUTHOR]