Synthesis of magnetic cobalt Nanoparticles anchored on graphene nanosheets and catalytic decomposition of orange II

Magnetic cobalt nanoparticles (NPs) at a size of approximately 29.9 nm anchored on graphene sheets were prepared and tested for heterogeneous oxidation of a dyeing pollutant, Orange II, with peroxymonosulfate (PMS) in aqueous solutions. The physicochemical properties of Co–graphene hybrids were investigated by various characterization techniques, such as powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometer (EDS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The incorporation of Co NPs and graphene sheets produces much higher catalytic activity of Orange II degradation than pure Co. The Orange II decomposition rate increases with increasing temperature (25–45 °C), pH (4–10), and PMS dosage (0.04–0.60 g/L) but decreases with its increased concentration (30–120 mg/L). Kinetic studies show decomposition of Orange II on Co–graphene can be described by a pseudo-first-order kinetic model with activation energy of 49.5 kJ/mol

A matter of space and time: How frequent is convergence in lithic technology in the African archaeological record over the last 300 kyr?

Stone artefacts are frequently used to identify and trace human populations in the Paleolithic. Convergence in lithic technology has the potential to confound such interpretations, implying connections between unrelated groups. To further the general theoretical debate on this issue, we first delineate the concepts of independent innovation, diffusion and migration and provide archaeological expectations for each of these processes that can create similarities in material culture. As an empirical test case, we then assess how these different mechanisms play out in both space and time for lithic technology across several scales of the African Stone Age record within the last 300 thousand years (kyr). Our findings show that convergence is neither the exception nor the norm, but a scale-dependent phenomenon that occurs more often for complex artefacts than is generally acknowledged and in many different spatio-temporal contexts of the African record that can crosscut the MSA/LSA boundary. Studies using similarly-looking stone tools to recognize past populations and track human dispersals in the Stone Age thus always need to test for the potential of independent innovation and not assume migration or diffusion a priori