Synthesis, characterization and catalytic properties of cobalt oxide recovered from spent lithium-ion batteries

Synthesis of Co,Ce Oxide Nanoparticles Using an Aerosol Method and Their Deposition on Different Structured Substrates for Catalytic Removal of Diesel Particulate Matter

The synthesis of Co and Ce oxide nanoparticles using precipitation of precursor salt solutions in the form of microdroplets generated with a nebulizer proved to be an efficient, fast and inexpensive method. Different morphologies of single oxides particles were obtained. Ceria nanoparticles were almost cube-shaped of 8 nm average size, forming 1.3–1.5 μm aggregates, whereas cobalt oxide appeared as rounded-edged particles of 37 nm average size, mainly forming nanorods 50–500 nm. Co3O4 and CeO2 nanoparticles were used to generate structured catalysts from both metallic (stainless steel wire mesh monoliths) and ceramic (cordierite honeycombs) substrates. Ceria Nyacol was used as a binder to favor the anchoring of catalytic particles thus enhancing the adhesion of the coating. The resulting structured catalysts were tested for the combustion of diesel soot with the aim of being used in the regeneration of particulate filters (DPFs). The performance of these structured catalysts was similar to or even better than that exhibited by the catalysts prepared using commercial nanoparticles. Among the catalysts tested, the structured systems using ceramic substrates were more efficient, showing lower values of the maximum combustion rate temperatures (TM = 410 °C).

Mechanochemically assisted persulfate activation for the facile recovery of metals from spent lithium ion batteries

A novel mechanochemically assisted persulfate activation method was proposed in this study to enhance the leaching of valuable metals from lithium-ion batteries by combining ball-milling, advanced oxidation processes and sucrose reduction. By optimizing leaching parameters including temperature, pH, milling time and solid-to-liquid ratio, high leaching efficiencies of 97.1%, 94.0%, 87.6% and 93.8% can be achieved for Li, Ni, Co and Mn respectively. In the mechanochemical process, the breakage of covalent bonds in cathode material is facilitated by free radicals generated from zero valent iron activated ammonia persulfate as well as mechanochemical activation. To further explore the role of free radicals, the mechanism of ammonia persulfate activation by zero valent iron was elucidated, and SO₄^•- was identified as the dominant reactive oxygen species in the mechanochemical process. Meanwhile, the synergistic effect of mechanochemically driven crystal dissolution and sulfate radical facilitated bond cleavage was revealed by ab initio molecular dynamics simulation. Moreover, the released metal was reduced by sucrose to a lower valent state of high solubility to promote transfer to the aqueous phase during the subsequent leaching process with dilute sulfuric acid. In this work, the insight on the mechanism of mechanochemical processes strengthened by free radicals may provide an inspiration for the recovery of valuable metals from LIBs.

How Chemoresistive Sensors Can Learn from Heterogeneous Catalysis. Hints, Issues, and Perspectives

The connection between heterogeneous catalysis and chemoresistive sensors is emerging more and more clearly, as concerns the well-known case of supported noble metals nanoparticles. On the other hand, it appears that a clear connection has not been set up yet for metal oxide catalysts. In particular, the catalytic properties of several different oxides hold the promise for specifically designed gas sensors in terms of selectivity towards given classes of analytes. In this review, several well-known metal oxide catalysts will be considered by first exposing solidly established catalytic properties that emerge from related literature perusal. On this basis, existing gas-sensing applications will be discussed and related, when possible, with the obtained catalysis results. Then, further potential sensing applications will be proposed based on the affinity of the catalytic pathways and possible sensing pathways. It will appear that dialogue with heterogeneous catalysis may help workers in chemoresistive sensors to design new systems and to gain remarkable insight into the existing sensing properties, in particular by applying the approaches and techniques typical of catalysis. However, several divergence points will appear between metal oxide catalysis and gas-sensing. Nevertheless, it will be pointed out how such divergences just push to a closer exchange between the two fields by using the catalysis knowledge as a toolbox for investigating the sensing mechanisms.