Preparation, modification and adsorption properties of spinel-type H 1.6 Mn 1.6 O 4 lithium-ion sieves with spiny nanotube morphology

H 1.6 Mn 1.6 O 4 lithium-ion sieve with spinel structure was successfully prepared by hydrothermal, high-temperature calcination and ion exchange reaction. XRD, SEM, TEM, N 2 ad/desorption and FTIR methods were employed to characterize the microstructure and morphology of the synthesized materials in detail. The experimental results show that H 1.6 Mn 1.6 O 4 has the characteristics of mesoporous structure and nanotube morphology with length of ∼ 10 μm and diameter of 500–700 nm, and the spiny structure was grown on the surface of the nanotube uniformly. The effect of Al 3+ doping on the structure and morphology of H 1.6 Mn 1.6 O 4 was studied. The results show that Al 3+ doping does not change the microstructure and morphology of H 1.6 Mn 1.6 O 4 , but the specific surface area and pore volume are increased to a certain extent. H 1.6 Mn 1.6 O 4 and H 1.6 Mn 1.6−x Al x O 4 were used as lithium-ion adsorbents to study the adsorption properties of Li + in solution. The adsorption experiment results show that the adsorption capacity of H 1.6 Mn 1.6 O 4 increased with increasing solution pH value, indicating that the strong alkaline solution with higher pH value is more favorable for Li + adsorption. The adsorption isotherm results show that Li + adsorption process was fitted well by Langmuir model, indicating that Li + maybe adsorbed on the surface of manganese oxides lithium-ion sieves via a monolayer adsorption. The theoretical maximum adsorption capacity of H 1.6 Mn 1.6 O 4 and H 1.6 Mn 1.6−x Al x O 4 can reach 39.54 mg/g and 40.54 mg/g, respectively. The results of adsorption kinetics show that the adsorption rate of both H 1.6 Mn 1.6 O 4 and H 1.6 Mn 1.6−x Al x O 4 is fast, and the adsorption capacity of H 1.6 Mn 1.6−x Al x O 4 (24.65 mg/g) is slightly better than H 1.6 Mn 1.6 O 4 (24.33 mg/g). Li + adsorption process can be well described by the pseudo-second-order model, suggesting adsorption behavior is mainly controlled by chemical sorption. Additionally, the free energy change (Δ G Θ ) was determined by Van't Hoff equation is negative, which confirms the adsorption process is spontaneous and feasible. The positive value of Δ S Θ of adsorption reaction reflects there is a certain of affinity between manganese oxides lithium-ion sieves and Li + in solution. Graphical Abstract The regular spiny structure on the surface of H 1.6 Mn 1.6 O 4 nanotube lithium-ion sieve was synthesized. This special morphology not only keeps the nanotube pore structure to increase the adsorption ability and also increases the outer surface area to accelerate the Li + diffusion speed without any substrate.