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Abstract: Toward the efficient and cost effective synthesis of three-dimensional hierarchical architectures at mild condition and their potential applications in environmental protection, the materials chemistry for green synthesis of strontium carbonate (SrCO3) superstructures and their application as adsorbents for methylene blue solution and heavy metal ions were explored. Uniform hierarchical mesoporous SrCO3 microspheres with a narrow diameter distribution were synthesized via a mild hydrothermal treatment (110°C, 6.0h) of the slurry derived from the room temperature coprecipitation of SrCl2 and Na2CO3 solution, in the presence of ethylenediaminetetraacetic acid (EDTA). The as-synthesized mesoporous SrCO3 microspheres had a specific surface area of 56.3m2 g−1 and a narrow pore size distribution concentrating on 2–20nm, with an average pore diameter of 9.45nm. The introduction of EDTA in due case with tuned pH value was favorable for the formation of SrCO3 microspheres, whereas the mild hydrothermal treatment promoted the morphology uniformity of the mesoporous microspheres with narrow diameter distribution. The adsorption evaluation indicated that the present mesoporous SrCO3 microspheres exhibited excellent adsorption performance for deionized (DI) water containing methylene blue, or heavy metal ions such as Fe3+ and Pb2+, revealing the as-synthesized uniform hierarchical mesoporous SrCO3 microspheres as potential adsorbents with wide applications in environmental protection. [Copyright &y& Elsevier]

Water pollution has become one of the most urgent environmental issues to be solved for the global society, how to rapidly and efficiently dispose of dye such as RhB-contaminated effluents has become an imperative issue from an environmental point of view. In this contribution, uniform mesoporous Mg 3 Si 2 O 5 (OH) 4 microspheres (88.0% of which have a diameter of 1.22–1.78 μm, S BET = 281.68 m 2 g −1 ) consisted of nanosheets have been synthesized via a facile H 3 BO 3 assisted cost-effective eco-friendly hydrothermal process (180 °C, 12.0 h), using abundant SiO 2 , MgCl 2 ·6H 2 O, and NaOH as the raw materials. Based on the effects of process parameters, the H 3 BO 3 assisted SiO 2 template-formation mechanism is investigated in detail, and especially the key role of H 3 BO 3 as the inorganic director/quasi surfactant is illustrated. When employed as the adsorbents for removal of RhB, the adsorption isotherm is well described by the Langmuir adsorption model, with the maximum monolayer adsorption capacities of 300.08 mg g −1 (higher than most of the referenced adsorbents). Meanwhile, the intra-particle diffusion model also well fits to the kinetic data, suggesting the diffusion within the mesopores of the rate-limiting step. Moreover, the recycling performance reveals the as-obtained mesoporous microspheres as highly efficient adsorbents for removal of RhB with satisfactory chemical, morphological and structural stability. [ABSTRACT FROM AUTHOR]

Originated from the by-product of alumina production, red mud has caused severe impact on environment. To cope with the increasingly urgent environmental issue, red mud has now been utilized for the first time to obtain the hierarchical porous γ-AlOOH/γ-Al 2 O 3 microspheres as high efficient adsorbents for dye removal. The NaAlO 2 leached from the red mud is hydrothermally treated at 150 °C for 6.0 h in the presence of urea, leading to hierarchical porous γ-AlOOH microspheres, with a specific surface area of 76.8 m 2 g −1 , 93% of which have a diameter within the range of 3.5–7.5 µm. The subsequent mild thermal conversion at 600 °C for 2.0 h results in the hierarchical porous γ-Al 2 O 3 microspheres with a specific surface area of 158.6 m 2 g −1 , and ca. 92% of which bear a size of 3.0–7.0 µm. The porous γ-AlOOH and γ-Al 2 O 3 microspheres exhibit excellent adsorption for MB with the maximum adsorption capabilities of 953.0 mg g −1 and 1587.6 mg g −1 , respectively, and the latter is distinctly higher than most of the reported results. The possible formation is proposed, and the adsorption mechanism is discussed. The present work provides a new insight into the comprehensive utilization of the red mud as great potential adsorbents for removal of anionic dyes from mimetic waste water, and also is helpful for the future potential applications of the unique hierarchical porous structures in catalysis and other related fields. [ABSTRACT FROM AUTHOR]

Developing suitable and efficient adsorbents to remove organic dyes from wastewater become a hot topic. Herein, core-shell sp3@sp2 nanocarbons (ND-700, ND-900, ND-1100 and ND-1300), consisting of diamond core and graphitic shell with variable sp2/sp3-carbon ratio, were prepared by annealing nanodiamonds (NDs) at various temperatures (700–1300 °C). The increased graphitization degree of the nanocarbons with the increase of annealing temperature was confirmed by X-ray diffraction (XRD) and high-resolution Transmission Electron Microscopy (HRTEM). Sequentially, these nanocarbons were utilized as solid adsorbents to remove anionic methylene orange (MO) and cationic methylene blue (MB). Results show that although all of the nanocarbons are positively charged, the nanocarbons with higher graphitization (ND-1100, ND-1300) exhibit higher adsorption performance for both MB and MO. This can be attributed to the forming of π-π interaction between the graphitic surface and aromatic rings within the dye molecules. The ND-700 exhibits little adsorption for cationic MB for its low graphitization as well as electrostatic repulsion. The adsorption of MO and MB on ND-700 and ND-1300 in the binary MO/MB system was also investigated, respectively. Results show that the ND-1300 could adsorb MO and MB efficiently and simultaneously, and ND-700 exhibits selective adsorption for MO from the binary system. [Display omitted] ● Core-shell sp3@sp2 nanocarbons with various graphitization were prepared. ● The sp3@sp2 nanocarbons showed graphitization-responsive feature for dye adsorption. ● Selective and simultaneous adsorption were observed in the binary MO/MB system. ● Selective adsorption to MO was observed on the nanocarbon with low graphitization. ● Simultaneous adsorption was observed on the nanocarbon with high graphitization. [ABSTRACT FROM AUTHOR]

Hierarchical three-dimensional (3D) porous structures are of great significance for their versatile applications in diverse fields. Herein, uniform Ca 4 B 10 O 19 ·7H 2 O microspheres were successfully fabricated via a facile hydrothermal method, followed by a thermal conversion (700 °C, 2.0 h) without any additives, leading to the 3D hierarchical porous calcium metaborate (Ca(BO 2 ) 2 ) microspheres with well-preserved spherical morphology and high crystallinity. When employed as adsorbents, the adsorption isotherms of Pb 2+ and Cd 2+ onto porous Ca(BO 2 ) 2 microspheres were well fitted with the Langmuir adsorption model, giving rise to the maximum adsorption capacities for Pb 2+ and Cd 2+ as 140.2 and 110.6 mg g −1 , respectively. When utilized as catalyst support, the good dispersion and smaller size of metallic Pd nanoparticles (NPs) as well as more and stronger acid sites on the catalyst resulted in the 1.05 wt% Pd/Ca(BO 2 ) 2 catalyst, by using which the conversion of benzyl alcohol and selectivity to benzaldehyde with O 2 as oxidant reached 94.3% and 96.0%, respectively. The resultant supported catalyst also exhibited satisfactory high conversion and especially excellent selectivity during 10 cycles of catalysis, revealing the as-prepared porous Ca(BO 2 ) 2 microspheres as superior catalyst carrier. The present hierarchical porous Ca(BO 2 ) 2 microspheres afforded promising and competitive candidates for water treatment and heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

Towards the malignant impact of red mud on the environment and water pollution caused by organic dyes, affluent residual iron ions in red mud are recovered and converted into functional hierarchical porous α-Fe 2 O 3 microspheres (HP α-Fe 2 O 3 MSs) comprising nanosheets (S BET : 78.75 m2 g−1, pore volume: 0.35 cm3 g−1, mean pore diameter: 15.92 nm) via a facile hydrothermal route (180 °C, 12.0 h), with the presence of urea and CTAB. When employed as the adsorbents for Congo red (CR) in simulated wastewater, the adsorption isotherm is well fitted with Langmuir isotherm model, and the corresponding maximum adsorption capacity is determined as 342.57 mg g−1, superior to that of most referred adsorbents in literatures. Meanwhile, the adsorption kinetic data can be well interpretated via the pseudo-second-order and intra-particle diffusion models. Moreover, the red mud derived HP α-Fe 2 O 3 MSs can be easily regenerated and reused with satisfactory chemical, morphological and structural stability. Affluent residual iron in red mud is extracted for the facile green hydrothermal synthesis of the hierarchical porous α-Fe 2 O 3 microspheres as efficient adsorbents for removal of Congo red, with excellent adsorption capacity and satisfactory recycling performance. Image 1 • Abundant iron in red mud is hydrothermally converted into hierarchical porous α-Fe 2 O 3 microspheres. • Adsorption isotherm can be well fitted with Langmuir isotherm model, with the q m determined as 342.57 mg g−1. • Microspheres can be easily regenerated and reused with satisfactory chemical, morphological and structural stability. • Major phase of the quasi amorphous iron-bearing room temperature precipitate is determined as Fe(OH) 3. • Adsorption kinetic data can be well interpretated via the pseudo-second-order and intra-particle diffusion models. [ABSTRACT FROM AUTHOR]

• A facile green rotating hydrothermal process is developed for quasi waxberry-like Ba 5 Si 8 O 21 microspheres. • Ba 5 Si 8 O 21 microspheres are formed at lower temperature with miniaturization of size in the absence of any surfactants. • A probable heat and mass transport enhanced rotating hydrothermal formation mechanism is proposed. • The microspheres exhibit high adsorption performance for CR (q m : 1238.7 mg g−1) with satisfactory stability and reusability. • The adsorption mechanism is systematically and deeply investigated. Towards the imperative water contamination by organic dyes, uniform hierarchical quasi waxberry-like Ba 5 Si 8 O 21 microspheres (diameter: 0.65–1.30 µm) consisted of nanorods have been successfully synthesized via a facile eco-friendly and cost-effective rotating hydrothermal process (120 °C, 6.0 h) without any organic additives, templates or surfactants, using abundant BaCl 2 ·2H 2 O and Na 2 SiO 3 ·9H 2 O as the raw materials. Based on the impacts of the process parameters, a probable heat and mass transport enhanced rotating hydrothermal formation mechanism is proposed. The rotating homogeneous hydrothermal reactor provides vigorous macro- and micro-mixing of the solid and solution phase, thus favors the early stage dissolution-recrystallization, formation of the product nuclei at lower temperature, and final self-assembly for uniform waxberry-like microspheres with miniaturization of size. When employed as the adsorbents for the elimination of Congo red (CR) from simulated waste water, the adsorption data are well fitted with Langmuir isothermal model (q m : 1238.7 mg g−1). Meanwhile, the adsorption of CR is well described by the pseudo-second-order kinetic and intra-particle diffusion models, indicating the final diffusion at equilibrium stage within the mesopores of the real rate-limiting step in the whole adsorption process. The recycling test further confirms the Ba 5 Si 8 O 21 microspheres as highly efficient adsorbents with satisfactory stability and reusability. As a noteworthy methodology, the heat and mass transport enhanced rotating hydrothermal synthesis presents new insights into the hierarchical porous silicate microspheres as a competitive candidate adsorbent for organic dyes removal, and also a potential new platform for heterogeneous catalysis. [ABSTRACT FROM AUTHOR]