An Application of a LPWAN for Upgrading Proximal Soil Sensing Systems.

In recent years, the Internet of Things (IoT), based on low-power wide-area network (LPWAN) wireless communication technology, has developed rapidly. On the one hand, the IoT makes it possible to conduct low-cost, low-power, wide-coverage, and real-time soil monitoring in fields. On the other hand, many proximal soil sensor devices designed based on conventional communication methods that are stored in an inventory face elimination. Considering the idea of saving resources and costs, this paper applied LPWAN technology to an inventoried proximal soil sensor device, by designing an attachment hardware system (AHS) and realizing technical upgrades. The results of the experimental tests proved that the sensor device, after upgrading, could work for several years with only a battery power supply, and the effective wireless communication coverage was nearly 1 km in a typical suburban farming environment. Therefore, the new device not only retained the original mature sensing technology of the sensor device, but also exhibited ultralow power consumption and long-distance transmission, which are advantages of the LPWAN; gave full play to the application value and economic value of the devices stored in inventory; and saved resources and costs. The proposed approach also provides a reference for applying LPWAN technology to a wider range of inventoried sensor devices for technical upgrading.

Restricted fiber contraction during amidoximation process for reinforced-concrete structured nanofiber sphere with superior Sb(V) adsorption capacity.

Amidoxime-polyacrylonitrile (APAN) nanofiber possesses advantages of adsorbing heavy metals for abundant amidoxime groups. However, it easily suffers from poor mechanical property caused by fiber contraction during amidoximation process. Inspired by high mechanical strength of reinforced concrete, we embedded stiff polylactic acid (PLA) skeletons into PAN matrix to prepare reinforced-concrete structured nanofiber sphere (APAN/PLA NFS) through solution blending. Preparation parameters including polymer concentration and PAN/PLA ratio were optimized as 4.0% and 1:1, and coarse sphere surface, numerous mesopores and large pore volume (19.3 mL/g) were endowed. Scanning electron microscope results showed restricted fiber contraction with nitrile conversion of 58.1%. APAN/PLA NFS showed robust compressive strength of 3.28 MPa with strain of 80%, and X-ray diffraction and differential scanning calorimeter analysis revealed that crystalline PLA reinforced non-crystalline PAN through molecule-level compatibility. Compared with plain APAN sphere, Sb(V) adsorption from water for APAN/PLA NFS showed better performance with superhigh capacity of 949.7 mg/g and fast rate (equilibrium time of 2 h), which was owing to abundant mesopores preserved by PLA skeletons. These findings indicated that PLA was a promising skeletal candidate which could protect APAN from fiber contraction during amidoximation process and could strongly expand adsorption capacity of APAN for heavy metals.

Adsorption of antimonite and antimonate from aqueous solution using modified polyacrylonitrile with an ultrahigh percentage of amidoxime groups.

Porous modified polyacrylonitrile (PAN) with an ultrahigh percentage of amidoxime groups (UAPAN) was synthesized for the first time and used to adsorb antimonite (Sb(III)) and antimonate (Sb(V)) from aqueous solution. Fourier transform infrared (FT-IR), Zeta potential, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) were adopted to characterize UAPAN and explore adsorption mechanism. Moreover, batch experiments were performed to investigate the influence of various adsorption parameters, including initial pH, contact time, temperature, coexisting ions and reusability on adsorption capacities. Results showed that the maximum adsorption capacities for Sb(III) and Sb(V) were 125.4 and 177.3 mg g-1, respectively, which were much higher than those of other adsorbents reported in literature. The adsorption thermodynamics was evaluated, indicating the spontaneous and endothermic adsorption. The adsorption isotherm was suitable to be modeled by Langmuir isotherm (R2 > 0.96). Results of FT-IR, Zeta potential and XPS indicated that adsorption was involved with electric charge attraction and ligand exchange. DFT further explained that better adsorption of Sb(V) on UAPAN than that of Sb(III) was caused by the higher adsorption energy, more favorable bond lengths and atom charge density. Accordingly, UAPAN is expected to be a compelling candidate for antimony decontamination from aqueous environment.