Temperature-dependent magnesium citrate modified formation of MgO nanoparticles biochar composites with efficient phosphate removal.

Nano-MgO biochar composites (nMBCs) have been considered as potential adsorbents for phosphate removal from aqueous solution. It is an effective strategy to improve P removal efficiency that adjustment of the size, distribution and crystallinity of MgO particles embedded into the carbon matrix. Herein, we prepared a highly efficient phosphate adsorbent by co-pyrolysis of lotus seedpod and magnesium citrate and studied its adsorption mechanisms. Results showed that the uniformly dispersed MgO nanoparticle was formed on the surface of nMBCs with the temperature increasing, with the particles size ranging from 3 to 10 nm. Furthermore, high temperature promoted the formation of a large amount of reactive lattice oxygen, which was demonstrated to be the main active adsorption site, thus the phosphate immobilization capacity of nMBCs was greatly improved with the pyrolysis temperature increasing from 450 °C to 750 °C. Besides, some stable CO bonds were formed due to the catalysis of Mg2+, which could bond to HPO42-/H2PO4- by hydrogen bond, enhancing the adsorption performance. The isotherm adsorption experiment showed that MBC-750 achieved an excellent phosphorus adsorption amount of 452.752 mg-P/g. The effectiveness of nMBCs is enhanced and a method for producing an effective nanocomposite adsorbent material for removing phosphate from wastewater is provided.

Nano nickel embedded in N-doped CNTs-supported porous biochar for adsorption-reduction of hexavalent chromium.

Nitrogen-doped carbon coated transition metal hybrids for the removal of hazardous hexavalent chromium (Cr(VI)) has attracted increasing attention in wastewater treatment recently. In this study, three-dimensional nano-nickel particles embedded in N-doped carbon nanotubes supported on porous biochar (Ni@N-K-C) were synthesized by a two-stage strategy of KOH activation followed by annealing. The effect of KOH activation treatment on the doping process and Cr(VI) removal properties were investigated. The results indicate that KOH activation can improve the pore parameters and promote subsequent doping of Ni and N and the growth of carbon nanotubes (CNTs). After KOH pretreatment, the specific surface area of Ni@N-K-C increased significantly to 604.62 m2/g. The improved pore structure accelerates the mass diffusion of Cr(VI) ions and provides an available surface for the adsorption and reduction of Cr(VI). Therefore, the Ni@N-K-C obtained at 900 °C showed a high removal capacity for Cr(VI) (824.4 mg/g) and a stronger ability to reduce to Cr(III).

Synergetic effect of magnesium citrate and temperature on the product characteristics of waste lotus seedpod pyrolysis.

To understand the synergetic effect of magnesium citrate (MC) and temperature on biomass pyrolysis, co-pyrolysis of lotus seedpod (LS) and MC was carried out in a fixed bed reactor. With the addition of MC, CO2 become the dominate composition in gas (55.83-90.75 vol%). And with temperature increasing, the main components in bio-oil converted from carboxylic acid to phenols and aromatics. Meanwhile, the mesoporous carbon was formed, with the BET specific surface area up to 514.66 m2/g, and pore diameter mainly focused at 3-8 nm. For the catalytic effect, the secondary cracking of pyrolytic volatiles (acetic acid and anhydrosugar) was inhibited, therefore the gas releasing was inhibited below 550 °C. However, at higher temperature, MgO catalysts favored the reduction of acids and deoxygenation via ketonization and aldol condensation reactions. The formed MgO as a template and the catalysis of MgO during co-pyrolysis contributed to the mesoporous structure of solid char.

Synthesis and characterization of magnesium oxide nanoparticle-containing biochar composites for efficient phosphorus removal from aqueous solution.

The effective removal and recovery of phosphorus from aquatic environments are highly important for successful eutrophication control and phosphorus recycling. Herein, we prepared biochar containing MgO nanoparticles (MgO-biochar) by fast pyrolysis of MgCl2-impregnated corn stalks, probed its phosphate adsorption performance. Through the fast pyrolysis, the MgCl2 promoted the formation of micropores and mesoporous, and decomposed into MgO nanoparticles with the size smaller than 100 nm. The adsorption experiments showed that the adsorption property increased with the increase of Mg content, and had a strong correlation with the external surface area. And the phosphate adsorption was well described by the Langmuir-Freundlich model (maximum adsorption capacity was determined as 60.95 mg P/g). Kinetic analysis and characterization analysis of MgO-biochar for different adsorption time indicated that phosphate adsorption onto MgO-biochar was mainly controlled by rapid binding to the external surface (about 75% of the equilibrium adsorption amount), and the uptake rate was limited by the slow diffusion of phosphate into the biochar interior (about 25% of the equilibrium adsorption amount). The results suggested that the synthesized MgO-biochar with enough MgO active site dispersed on a higher external surface can be used as a potential adsorbent for phosphate removal and recovery from aqueous solution.

[Preparation of MgO Modified Lotus Shell Biochar and Its Phosphorus Adsorption Characteristics].

To study the potential application characteristics of biochar as a phosphate adsorbent, nano-MgO-biochar was prepared by rapid pyrolysis of a mixture of MgO and lotus shells. The physicochemical properties were characterized by XRD, BET, SEM, and TEM, and adsorption experiments were conducted. The results showed that MgO was mainly supported on the surface of carbon in the form of flakes and granules, which increased the adsorption active site, and the adsorption amount of MgO-biochar MBC3 was 14 times higher than that of biochar MBC1 without MgO. The adsorption capacity of MBC9, which was prepared by rapid pyrolysis under 10% CO2 atmosphere, was further increased 16 times higher than that of MBC1. The adsorption kinetics followed a pseudo-second-order model, which indicated the adsorption of phosphate on MgO-biochar was dominated by chemical adsorption. According to the Langmuir equation, the maximum adsorption capacity of MBC3 and MBC9 could reach 283.26 mg·g-1 and 297.96 mg·g-1, respectively. MgO-biochar is a high-efficiency phosphate adsorbent, which can be used to control the eutrophication of water.

The densification of bio-char: Effect of pyrolysis temperature on the qualities of pellets.

The densification of bio-chars pyrolyzed at different temperatures were investigated to elucidate the effect of temperature on the properties of bio-char pellets and determine the bonding mechanism of pellets. Optimized process conditions were obtained with 128MPa compressive pressure and 35% water addition content. Results showed that both the volume density and compressive strength of bio-char pellets initially decreased and subsequently increased, while the energy consumption increased first and then decreased, with the increase of pyrolysis temperature. The moisture adsorption of bio-char pellets was noticeably lower than raw woody shavings but had elevated than the corresponding char particles. Hydrophilic functional groups, particle size and binder were the main factors that contributed to the cementation of bio-char particles at different temperatures. The result indicated that pyrolysis of woody shavings at 550-650°C and followed by densification was suitable to form bio-char pellets for application as renewable biofuels.