•MB removal by ferrite nanocomposites was enhanced by microwave heating.•The pH values of MB solutions inclined to 7 after microwave treatment of ferrite.•The dimethylamino group in MB molecule is easier and prior to be degraded.•The max MB removal was 99.7%, among which >46.8% molecules were completely degraded.Developing rapid and effective methods to remove dyes from water has gained global concerns. In this study, we prepared porous MnFe2O4 (RMN) and porous CoFe2O4 nanocomposite (RCN) with high BET surface area and pore volume using rice hull, and investigated their catalytic degradation and degradation mechanisms for methylene blue (MB). Under microwave heating, the MB removal by RMN and RCN was accelerated and enhanced significantly due to the selective heating and enhanced catalytic degradation activities. The MB removal fits pseudo-second-order model. The removal rate increases with sample dosage, microwave output power, and initial pH value. The resulting pH value was inclined to neutral after microwave treatment. The dimethylamino including methyl groups in MB molecule are easier and prior to be degraded by ferrite nanoparticles in the nanocomposites during either adsorption or microwave treatments. According to the resulting concentrations of MB, NO3−, and SO42−, the maximum MB removal achieved 99.7%, among which more than 46.8% molecules were completely degraded. This study provided essential information on the degradation behavior and mechanism of basic dyes by microwave-enhanced ferrite treatments and also supplied a potential rapid and effective method to remove organic contaminants from aqueous solutions.

We synthesized novel magnetic nanotubular encapsulates with ferrite nanoparticles embedded into the inner channels of halloysite nanotubes (HNTs) for the first time. The nano-encapsulates with enclosed ferrite nanoparticles show significantly enhanced magnetic and electromagnetic performance when compared to that with external particles.

Strong absorption, low density, and thin matching thickness are important parameters for electromagnetic (EM) wave absorbers. In this study, we prepared novel porous magnetic nanocomposites using corncob powders as template. The presence of corncob will significantly decrease the bulk density of samples from more than 4.0 to about 0.55 g cm−3. The porous structures remarkably decreased the permittivity (ε) and permeability (μ) and enhanced the impendence matching between the absorber and air. The porous magnetic nanocomposites exhibit enhanced absorption for EM waves at thin matching thickness. The optimum thickness is only 1.0–1.4 mm, with bandwidth of RL < −5 dB of about 8 GHz, covering the half X-band and the whole Ku-band. The areal density of magnetic absorbers at this study is only about 0.7–1.0 kg m−2 at thickness of 1.0–1.4 mm, much lower than the reported values of other magnetic absorbers. Due to the strong absorption at low density and thin matching thickness, the porous magnetic nanocomposites prepared using corncob powders as template are promising light-weight EM wave absorbers.Highlights► We prepared novel porous magnetic nanocomposites using corncob as template. ► The presence of corncob will decrease the bulk density of FeNi alloy from 4.1 to 0.55 g cm−3. ► The optimum matching thickness of the nanocomposites is only 1.0–1.4 mm. ► The nanocomposites show enhanced wide-band absorption for EM waves at 2–18 GHz.

In this study, we systematically investigated the effects of sulfuric acid treatment on the physico-chemical and pore characteristics of halloysite. XRD results indicate that sulfuric acid will destroy the crystal structure of halloysite and finally turn it into amorphous silica. The acid will react with halloysite nanotubes from both inner and outer surfaces, dissolve the [AlO6] octahedral layers and led to the rupture and collapse of [SiO4] tetrahedral layers. The BET surface area and total pore volume of halloysite increase firstly with treatment times from 1 to 13 h, and then start to decrease due to disaggregation of silica layers. The acid treated halloysites exhibit fixed micropore and controllable mesopore size distributions and are effective low-cost adsorbents. The maximum adsorption capacity of acid treated halloysite for methylene blue is more than 60 mg g−1 and can be controlled by pH values. Furthermore, the acid treated halloysite are potential supporters for enzyme, drug, sensors, and so on.Graphical abstractHighlights► We systematically analyzed the process of sulfuric acid reacted with halloysite. ► Sulfuric acid could react with halloysite directly and finally turned it into amorphous silica. ► TEM images confirmed the rupture and collapse of [SiO4] tetrahedral layers. ► The acid treated products have fixed micropore size and controlled mesopore size distribution.