A Super-Hygroscopic Solar-Regenerated Alginate-Based Composite for Atmospheric Water Harvesting

Global water scarcity is leading to increasingly tense competition across populations. In order to complement the largely fast-depleting fresh water sources and mitigate the challenges generated by brine discharge from desalination, atmospheric water harvesting (AWH) has emerged to support long-term water supply. This work presents a novel alginate-based hybrid material comprised of porous silico-aluminophosphate-34 (SAPO-34) as fast-transport channel medium as well as hydrophilicity and stability enhancer, and graphene-based sheets as light absorber for solar-enabled evaporation, both optimally incorporated in an alginate matrix, resulting in a composite sorbent capable of harvesting water from the atmosphere with a record intake of up to 6.85 gw gs -1. Natural sunlight is solely used to enable desorption achieving increase of the temperature of the developed network up to 60 °C and resulting in release of the sorbed water, with impurities content well below the World Health Organization (WHO) upper limits. After 30 cycles of sorption and desorption, the composite hydrogel displayed unchanged water uptake and stability. This work provides an impactful perspective toward sustainable generation of water from humidity without external energy consumption supporting the emergence of alternative water production solutions.

Sapo-34 Obtained from Amazonian Flint Kaolin: Influence of Impurities of “Oxidized Fe/Ti” in Synthesis and Its Application in the Removal of Cationic Dye from Water

Non-processed kaolin (flint kaolin) from a mine located in the Capim area (Amazon region, northern Brazil), usually considered as waste, was selected as a source of silicon and aluminum in the synthesis of SAPO-34. This is a molecular sieve and cationic exchanger chosen for tests focusing on the removal of methylene blue in aqueous solutions, which is a cationic dye widely used by textile industries in Brazil. The results revealed that the SAPO-34 has been successfully synthesized with typical cubic morphology, good crystallinity (>90%), and thermal stability (~998 °C). Although the oxidized Fe/Ti impurities contained in the flint kaolin affect the degree of crystallinity of the zeolitic product, its adsorptive properties are not significantly affected, which demonstrates the excellent adsorption results (pH = 11; % removal > 90%). It proved to be an adsorbent with considerable adsorption capacity (9.83 mg·g−1). The pH test confirmed the acidic surface characteristics (pH solution 2–4; ↓ removal), and the kinetic model that best fitted the experimental data was pseudo-second-order, with R2 = 0.998 (kinetics controlled by chemisorption).

Synthesis of SAPO-34 Nanoplates with High Si/Al Ratio and Improved Acid Site Density

Two-dimensional SAPO-34 molecular sieves were synthesized by microwave hydrothermal process. The concentrations of structure directing agent (SDA), phosphoric acid, and silicon in the gel solution were varied and their effect on phase, shape, and composition of synthesized particles was studied. The synthesized particles were characterized by various techniques using SEM, XRD, BET, EDX, and NH₃-TPD. Various morphologies of particles including isotropic, hyper rectangle, and nanoplates were obtained. It was found that the Si/Al ratio of the SAPO-34 particles was in a direct relationship with the density of acid sites. Moreover, the gel composition and preparation affected the chemistry of the synthesized particles. The slow addition of phosphoric acid improved the homogeneity of synthesis gel and resulted in SAPO-34 nanoplates with high density of acid sites, 3.482 mmol/g. The SAPO-34 nanoplates are expected to serve as a high performance catalyst due to the low mass transfer resistance and the high density of active sites.

Hydro-treating and Hydro-isomerisation of Sunflower Oil using Pt/SAPO-11: Influence of Templates in Ultrasonic Assisted with Hydrothermal Synthesis

Pt/SAPO-11 mesopores type materials has successfully synthesized using different templates, such as: diethylamine (DEA), dimethylamine (DMA), and n-propylamine (n-PA), under ultrasonication coupled with hydrothermal treatment or independently with hydrothermal treatment. The influences of structure directing agent (SDA) and synthesis method are investigated by different characterization techniques and the role of the material as catalyst in hydrotreating of sunflower oil has examined. The synthesized materials have been characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Fourier Transform Infra Red (FT-IR) techniques. It is found that SAPO-11 material which has synthesized with n-PA as a template has the characteristics of high silicon incorporation. Hydrotreating of sunflower oil is carried out in a fixed bed reactor with Pt impregnated SAPO-11 catalyst and a detailed study on the isomerization is performed by varying the operating parameters like temperature and space velocity. The high selectivity of Pt/SAPO-11 catalyst is achieved by uniform pore size and acidity. Also the pore opening of the catalyst has a major effect in the selectivity of the catalyst. Further, it represents a higher ratio of isomers compared to other synthesized catalysts on hydro-treating of sunflower oil.  Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

A mini-review on recent developments in SAPO-34 zeolite membranes and membrane reactors

Schematic diagram of a SAPO-34 membrane for various gas separation.

MOR/DEA/TEA mixed-template synthesis of CHA-type SAPO with different silica and alumina sources

SAPO-44 was firstly synthesized in a MOR/TEA/DEA mixed-template system. The effect of different Al and Si sources on the catalytic properties and MTO performance of the catalysts was significant.

The hydrothermal synthesis of hierarchical SAPO-34 with improved MTO performance

A two-step hydrothermal approach for the synthesis of hierarchical SAPO-34 in the absence of any mesoporogen.

Copper-Iron Bimetal Ion-Exchanged SAPO-34 for NH3-SCR of NOx

SAPO-34 was prepared with a mixture of three templates containing triethylamine, tetraethylammonium hydroxide, and morpholine, which leads to unique properties for support and production cost reduction. Meanwhile, Cu/SAPO-34, Fe/SAPO-34, and Cu-Fe/SAPO-34 were prepared through the ion-exchanged method in aqueous solution and used for selective catalytic reduction (SCR) of NOx with NH3. The physical structure and original crystal of SAPO-34 are maintained in the catalysts. Cu-Fe/SAPO-34 catalysts exhibit high NOx conversion in a broad temperature window, even in the presence of H2O. The physicochemical properties of synthesized samples were further characterized by various methods, including XRD, FE-SEM, EDS, N2 adsorption-desorption isotherms, UV-Vis-DRS spectroscopy, NH3-TPD, H2-TPR, and EPR. The best catalyst, 3Cu-1Fe/SAPO-34 exhibited high NOx conversion (> 90%) in a wide temperature window of 250–600 °C, even in the presence of H2O. In comparison with mono-metallic samples, the 3Cu-1Fe/SAPO-34 catalyst had more isolated Cu2+ ions and additional oligomeric Fe3+ active sites, which mainly contributed to the higher capacity of NH3 and NOx adsorption by the enhancement of the number of acid sites as well as its greater reducibility. Therefore, this synergistic effect between iron and copper in the 3Cu-1Fe/SAPO-34 catalyst prompted higher catalytic performance in more extensive temperature as well as hydrothermal stability after iron incorporation.