In this study, carbon nanotubes with Fe cores (Fe-CNTs) were successfully prepared by the vapor deposition method, which used raw coal as a carbon source. The brookite crystal Ti 3+ -doped TiO 2 (Ti 3+ -TiO 2 ) was obtained via thermal reduction with the reductant NaBH 4 . Then, it was loaded on Fe-CNTs to obtain Ti 3+ -TiO 2 /Fe-CNTs. While characterizing the structure of these prepared catalysts, the photocatalytic coreduction of N 2 /CO 2 was performed for the synthesis of urea (CO(NH 2)2 ) in H 2 O. The findings were as follows: (i) the reductant NaBH 4 could lead to the formation of the brookite crystal TiO 2 ; (ii) the main product of the photocatalytic coreduction N 2 /CO 2 in H 2 O is CO(NH 2 ) 2 , and it also includes the gas products (H 2 , CO, and O 2 ) and other liquid products (NH 4+ , NO 2 − , NO 3 − , C 3 H 6 O 2 , and C 4 H 8 O 2 ); (iii) the performance of photocatalytic co-reduction of N 2 /CO 2 to CO(NH 2 ) 2 in H 2 O was related to the arrangement of Ti 3+ sites and oxygen vacancies on the surface of Ti 3+ -TiO 2 . The Ti 3+ sites and oxygen vacancies act as the active centers for N 2 and CO 2 molecules, respectively. The adsorption and activation converted the N 2 and CO 2 molecules into six-membered cyclic intermediates, which further transformed into the CO(NH 2)2 product. In addition, the CO(NH 2 ) 2 yield of the composite photocatalyst can reach 710.1 μmol/(L g) in a 4 h reaction, with 4.6 times as the single Ti 3+ -TiO 2 , which shows that the Fe-CNT support is beneficial for the photocatalysis. KEYWORDS: coal, carbon nanotubes, Ti 3+ -doped TiO 2 , photocatalytic co-reduction N 2 /CO 2 , urea

No abstract

Biochar has been intensively investigated for carbon sequestration, soil fertility enhancement, and immobilization of heavy metals and organic pollutants. Large-scale use of biochar in agricultural production and environmental remediation, however, has been constrained by its high cost. Here, we demonstrated the production of low-cost biochar ($20/ton) in the field from Robinia pseudoacacia biowaste via a combined aerobic and oxygen-limited carbonization process and a fire-water-coupled method. It involved aerobic combustion at the outer side of biomass, oxygen-limited pyrolysis in the inner core of biomass, and the termination of the carbonization by water spray. The properties of biochar thus produced were greatly affected by exposure time (the gap between a burning char fell to the ground and being extinguished by water spray). Biochar formed by zero exposure time showed a larger specific surface area (155.77 m 2 /g), a higher carbon content (67.45%), a lower ash content (15.38%), and a higher content of carboxyl and phenolic-hydroxyl groups (1.74 and 0.86 mol/kg, respectively) than biochars formed with longer exposure times (5-30 min). Fourier-transform infrared spectroscopic (FTIR) spectra indicated that oxygen-containing functional groups of biochar played a role in Cd and oxytetracycline sorption though a quantitative relationship could not be established as the relative contribution of carbon and ash moieties of biochar to the sorption was unknown. Outcomes from this research provide an option for inexpensive production of biochar to support its use as a soil amendment in developing countries.