Nanofibers made of different materials have been continuously studied and widely used as membranes due to their simple fabrication techniques and tunable surface characteristics. In this work, we developed polyacrylonitrile (PAN) nanofiber membranes by the electrospinning method and blended them with polysulfone (PSU) to obtain superhydrophobic surfaces on the fiber structures. The scanning electron microscopy (SEM) images show that the fabricated nanofibers have smooth and continuous morphology. In addition, to observe the effect of the PSU-based blending material, Fourier-transform infrared (FTIR) spectra of the samples were acquired, providing chemical compositions of the bare and PSU-blended PAN nanofibers. The fabricated PSU/PAN composite nanofibers have a diameter range of 222-392 nm. In terms of the wettability, the measured water contact angle (WCA) value of the PAN nanofibers was improved from (14 +/- 1)degrees to (156 +/- 6)degrees, (160 +/- 4)degrees, (156 +/- 6)degrees, and (158 +/- 4)degrees after being blended with PSU solutions having concentrations of 0.5, 1, 1.5, and 2 wt %, respectively. This result has proven that the PAN nanofiber surfaces can be tuned from hydrophilic to superhydrophobic characteristics simply by introducing PSU into the PAN solution prior to electrospinning, where a small PSU concentration of 0.5% has been sufficient to provide the desired effect. Owing to its low-cost and highly efficient process, this strategy may be further explored for other types of polymer-based nanofibers.

Facile synthesis of reduced-graphene oxide (rGO) has been conducted in this study using the extract of Caesalpinia sappan L. as a green reducing agent. Graphite sheets were first exfoliated using an improved Hummer process to produce graphene oxide (GO). Then, the reduced-graphene oxide (rGO) was obtained by reducing GO with Caesalpinia sappan L. extract at various concentrations in an autoclave hydrothermal process. Analytical methods such as XRD, Raman spectroscopy, FTIR, SEM-EDX, TEM, UV–visible absorption, TG-DTA, and zeta potential value were used to characterize the graphite, GO, and rGO materials. A cyclic voltammetric study was also conducted to measure the performance of the synthesized materials. All rGO show good electrochemical properties, and the highest oxidation and reduction currents are observed for rGO-10. The characterization results show that Caesalpinia sappan L. extract can effectively reduce GO to rGO, and the best rGO can be obtained by adjusting the level of the extract.

A quartz crystal microbalance (QCM) system was modified with polyvinyl acetate nanofibers and doped with aniline for the detection of gaseous formaldehyde. The devised QCM gave a sensitivity of 0.056 Hz ppm −1 and is selective over other gases.

A novel bio-adsorbent was synthesized by the reaction between persimmon tannin (PT) and cobalt ferrite (CoFe2O4) with glutaraldehyde crosslinking, assigned as CoFe2O4@SiO2@PT. The product structure was confirmed by FTIR, XRD, TEM, DSC/TGA, and VSM. The results confirmed that the adsorbent had been successfully prepared and its surface had hydroxyl groups, which gave a great active site for Au(III) adsorption. As tested by batch system results, the kinetic data were consistent with the pseudo-second-order equation, while the adsorption equilibrium data fit well with the Langmuir model. The competitive adsorption test indicated that the adsorbent had a good preference to adsorb Au(III) over other coexisting ions. The Au(III) adsorption capacity of the adsorbent was 881.91 mg/g. It is greater than that of the reported adsorbents. The characterization by XRD, EDX, and SAED suggested that the adsorbed Au(III) was reduced to Au(0) particles as facilitated by the available functional groups. This adsorbent may be one of the good choices for the preconcentration and recovery of Au(III) from e-waste.

Solid hydrolysate and biochar 2:1 are synthetic humus from hydrothermal carbonization of chicken feather waste and contain humin that can be isolated by IHSS method. The recalcitrant humin is obtained in solid form. The yield of isolated humin from biochar 2:1 was 44.5%, and humin from solid hydrolysate was 12.7%. Analysis of humin by FTIR indicated the characteristics of complex functional groups. Based on the XRD and TEM tests, humin is formed from amorphous crystals with <14 nm in size and categorized as a superparamagnetic nanoparticle. The surface morphology of humin from solid hydrolysate is in the form of small spheres attached to larger particles, while humin from biochar 2:1 is smoother and has a larger surface area. This synthetic humin contains the nutrients N, O, Si, Cu, S, Mg, Zn, and K based on the EDX test quantitatively supported by AAS analysis. Characteristics of humin, which contains nutrients, are composed of amorphous crystals with complex functional groups during the hydrothermal carbonization process. Their relatively small heterogeneous molecules are stabilized by hydrophobic interactions and hydrogen bonds to form supramolecular compound associations in hour order. This humin content in synthetic humus is expected to increase its utility as a soil improver.

Reduced graphene oxide (rGO) has attracted much attention because of its high thermal conductivity, electrical properties, Young's modulus, mechanical strength, optical transmittance as well as theoretical areas. This material is widely used for various applications and normally produced by the reduction of graphene oxide (GO). Currently, the reducing agents used in the rGO synthesis such as hydrazine are harmful to the environment. Therefore, multiple searches for eco-friendly reducing agents have been conducted to replace the toxic ones. This brief review discusses the challenge of using natural extracts as reducing agents and several techniques commonly utilized in the synthesis of rGO from GO. Furthermore, the chemical components and mechanism involved in the reduction process are reviewed and compared. Some mechanisms involved in the GO reduction are discussed from the view point of the chemical contents in the plant extracts. Several fundamental characterization techniques, such as UV-Vis, FTIR, XRD, and Raman spectroscopies are also described. These main characterizations are utilized to justify the success of the reduction process with the hope that it can be used as an initial screening before a complete characterization of the synthesized rGO is conducted. Moreover, the developing use of natural reducing agents faces some challenges, including the complexity of the compounds in the natural extracts and the reproducibility of the synthesis method. This review summarizes the strategy for applying natural agents to reduce GO to rGO so that it can help researchers finding the novel green extracts and use it effectively in the rGO synthesis process.

Exfoliated graphene has been successfully synthesized using electrochemical exfoliation method followed by sonication of the graphite rod. Ammonium sulfate, sodium sulfate, ammonium oxalate, hydrogen peroxide, and ammonium persulfate were used as electrolytes. The effect of sonication time was studied for several products. The exfoliated graphene (EG) was characterized using XRD, Raman, FTIR, SEM-EDS, TEM and electrical con-ductivity measurement. The exfoliation using ammonium sulfate-ammonium persulfate as the electrolyte gives the highest mass-product, with a yield of almost 70%. Adding peroxide to the electrolyte reduces the mass of the exfoliated product. In addition, different sonication times results in different phenomena of particle size changes. The XRD data show that the EG has 2 theta = 26.4 degrees which is lower than its origin graphite. Raman data confirm that the EG has been obtained with the FWHM (G) value of 45-70 cm-1, and the resulting EG is a multilayer (2D peak). The O-H and C-C aromatic group has been assigned from FTIR spectrum. From SEM and TEM images, it was understood that the morphology of material is wrinkled, crumpled, and has a transparent zone, while from EDS data, it is found that the O/C value is in the range of 0.15-0.35. The electrical conductivity of EG reaches 52 S/cm.

Various ammonia sensors based on different materials have continuously been developed and employed to enable real-time monitoring of ammonia gas in the environment. Efforts are put not only to improve their sensitivity and selectivity towards the target gas but also to operate them at room temperature. Here, we investigated the effect of overlaying maltodextrin with different concentrations on the surface of polyvinyl acetate (PVAc) nanofibers on ammonia sensing performances, in which quartz crystal microbalance (QCM) was utilized as a transducer to measure the resonance frequency shift affected by the adsorbed gas molecules. Higher concentrations of the overlaying maltodextrin led to larger nanofiber diameter and more functional active groups on the active nanofibrous layers. PVAc nanofibers with 0.05% maltodextrin overlay demonstrated the highest sensitivity of 0.525 Hz center dot ppm(-1) at room temperature, which was 6.4 times higher than their bare counterpart (nanofiber without maltodextrin overlay). That sensor also possessed fast response and recovery times of 32 s and 17 s with a low detection limit (1.92 ppm). Besides its high reproducibility, reversibility, and repeatability, the sensor exhibited outstanding selectivity to other gas analytes and good long-term stability for 32 days of testing. This research shows that maltodextrin overlay can be used as a low-cost alternative route to increase the performance of organic material-based ammonia sensors, especially polymer nanofibers.

Modification of silica purified from the Merapi volcanic ash with magnetic material of Fe3O4 and attachment of cetyl triamine bromide (CTA-Br) on the magnetic cored has been performed to provide recoverable and positive surfaced of natural adsorbent. The magnetic cored was prepared via co-precipitation and CTA-Br attachment was conducted by a facile strategy. Then, the modified adsorbents were characterized by SEM, TEM, XRD, and FTIR instruments and examined for removing anionic Cr(VI) from the water media. The characterization data confirmed that crystals of Fe3O4 coated by SiO2 that has been bound with CTA-Br have been successfully formed. Additionally, increasing CTA-Br loaded gives thicker lamination on Fe3O4@SiO2/CTA-Br, but the CTA-Br loaded with higher than 0.25 mmol, leads to the coating peeled out. It is also demonstrated that Fe3O4@SiO2/CTA-Br prepared with CTA-Br 0.25 mmol is ideal for Cr(VI) anionic removal, regarding to the highest adsorption and very good separation or recovery process. Moreover, the optimal dose of Fe3O4@SiO2/CTA-Br in the Cr(VI) removal was observed at 0.25 g/20 mL under condition of pH 3 for 60 min. The adsorption of Cr(VI) well fits the Langmuir isotherm model with an adsorption capacity of 3.38 mg g-1 and is in a good agreement with pseudo-second order giving kinetic constant at 0.005 g mg-1 min-1. Thus, it is clear that the natural adsorbent material with recoverable properties for more efficient and wider application of removal Cr(VI) contaminant was expected from this study.

The current development of potentiometric taste sensing still adopts a liquid-contact design. However, works on potentiometric electrodes suggest a shift towards all-solid-state electrodes (ASSE) with the advantage of solving the liquid-contact limitations. Therefore, in this study, we explore the feasibility of a taste sensor using an ASSE design by utilizing a polypyrrole-carbon black (PPy-CB) composite as an ion-electron transducer. The sensor was fabricated by depositing an astringent-selective lipid/polymeric membrane on top of a glassy carbon-modified PPy-CB electrode. Methods of characterization including scanning electron microscopy, cyclic voltammetry, impedance spectroscopy, and chronopotentiometry, were systematically performed on the as-fabricated sensor. In summary, the sensor acts similarly to the ASSE-based ion-selective electrode in that the addition of the PPy-CB layer significantly improves the stability of the sensor, owing to its high capacitance. No evidence of a water layer presents beneath the membrane and the sensor could still retain stability despite interference from O2 and light. The fabricated sensor is highly reusable and exhibits linear behaviour toward standard astringent substance (tannic acid) in wide concentrations with a sensitivity of 17.997 mV/decade and R2 = 0.995 in the wide sensing range. The proposed sensor can also respond toward gallic acid and is highly selective against interfering tastes. This demonstrates that the taste sensor can be fabricated using ASSE design, which solves some limitations of the conventional liquid-contact electrode.

This research aims to determine the concentration of multi-nutrients and heavy metals and investigate the correlation among them in the seven inorganic fertilizers in Indonesia. Sample analysis was carried out using the NAA method. The highest concentrations of macro-nutrients were K (36.54 %) and Cl (18.09%) found in the KCl sample, while Ca (23.01%) was observed in the TSP sample. In the case of micro-nutrients, the highest concentrations of Se (0.36 mg/kg), Ti (597 mg/kg), Br (1.84%), and Ni (2.46 mg/kg) detected in the NPK sample. Meanwhile, the highest concentrations of Co (19.57 mg/kg) and Na (1.40%) were measured in the ZA sample, while Mg, with the highest concentration of 1.78%, was found in the KMgS sample. The micro-nutrients with the highest concentration detected in the TSP sample were Cr (45.96 mg/kg), Zn (342.6 mg/kg), and Mn (1331 mg/kg). Non-essential elements such as U, V, La, Sb, Sm, Th, Hf, Sr, Cs, Tb, Sc, Rb, Ta, and Eu were also detected in the fertilizer samples with the highest concentrations in the TSP sample. Statistical tests of multi-nutrient and heavy metals concentrations indicated that multi-nutrient and heavy metals in fertilizers are complex.

This study aims to identify the toxic heavy metals and trace elements in pesticides which are suspected to be a source of environmental pollution. The Neutron Activation Analysis method was used to identify and determine the concentration of toxic heavy metals and trace elements in pesticide samples. The pesticides used in this study consist of pesticides that are widely used by onion farmers in Brebes District, Central Java – Indonesia. These pesticides consist of two types (fungicides and insecticides) and in two different forms (solid and liquid). The results indicates that pesticides contain large levels of trace elements (Mg, Ti, Cl, Al, Ca, Br, Na, U, Mn, Br, La, Se, Hg, Rb, Fe, Eu, and Sb), and toxic heavy metals (As, Co, Cr, Ni, Zn, Cu, Hg). Generally, solid pesticides contain higher concentration of elements than liquid pesticides. In addition to releasing organic compounds, pesticides are also proven to be a source of certain trace elements (especially Mn, Br, Ti, Fe, Al) and toxic heavy metals (Cu, Zn, and Cr). They can affect the presence of these elements in the environment. *Corresponding author: sjuari@ugm.ac.id

In this chapter, some inorganic materials such as coal ash, hydroxyapatite, and hydrotalcite are taken up as the adsorbents to remove pollutants in contaminated water and soil. Coal ash is a residual material that exists after all combustible material in coal has been burned. The main components of coal ash are silica (SiO2) and alumina (Al2O3) and other metal oxides also exist. Although coal ash has some ability to adsorb pollutants, the ability increases by activation with acids and modification with an organic ligand like dithizone. The activated and modified coal ash were applied to the adsorption of cationic, anionic dyes and also Hg(II). Hydroxyapatite (HAP), one form of Ca-phosphate compound, is a main component in bone as well as collagen. HAP is an important material biologically and it becomes an excellent adsorbent for arsenate. Firstly, our studies of HAP as the geometrical scaffolds for bone reconstruction are introduced and then the removal of arsenate from environmental water by HAP is discussed using a chromatographic system. Lastly, the adsorbing property of layered double hydroxides (LDHs), which are called hydrotalcite minerals, with the unique structure, is discussed as well as the systhesis methods.

This research aims to synthesize silver nanoparticles (AgNPs) using Kirinyuh (Chromolaena odorata) leaf extract with different temperature and evaluate its activity in Vibrio sp. The synthesis was carried out by combining between silver nitrate solution and Kirinyuh leaf extract at room temperature (AgNPs 200) and hydrothermal process at 60oC (AgNPs 200*). Based on the results of LC-MS analysis, most of the chemical content of an extract was a flavonoid group compound. The color of the solution changed from colorless to red-brown, and a new peak around 435 nm showed that silver nanoparticles have been successfully obtained. The hydrothermal process exhibits sharp peaks rather than without hydrothermal treatment. The silver nanoparticles have a definite crystalline structure. The FTIR spectroscopy analysis indicated the organic compound was responsible for capping and stabilizing agents. In addition,TEM analysis showed that AgNPs 200 and AgNPs 200* exhibited average particle size of 32.89 nm and 27.82 nm, respectively. The presence of AgNPs can enhance the zone of growth inhibition of Vibrio sp approximately 300% compared to Kirinyuh leaf extract. Silver nanoparticles is estimated to possess the potential to be further evolved and utilized to inhibit the growth of Vibrio sp bacteria in shrimp agriculture.

Graphene and its derivates are among the emerging materials to be studied extensively for many electrochemical applications.The work's objective is to learn the hydroxyl functionalized graphene-modified electrode in the electrochemical oxidation of methylene blue, which is known as a significant industrial dye.Hydroxyl functionalized graphene (G-OH) has been synthesized using graphite as a precursor by a combination of electrochemical exfoliation and sonication methods.Graphite was electrochemically exfoliated in 1,0 M Li2SO4 solution for 2 h to produce oxidized graphene flakes.The oxidized graphene flakes were sonicated in 75% acetone for 2 h to yield G-OH.The product crystal structure and elemental composition were checked with XRD and SEM-EDX.The produced G-OH has an atomic content of C 77,98% and O 22,02%.We also confirmed the product by UV-Vis, FTIR, and Raman spectrometries.The G-OH was deposited on the stainless-steel electrode (SS) and tested in the electrochemical oxidation of methylene blue (MB).The cyclic voltammogram of the bare SS electrode and SS/G-OH modified electrode gives oxidation current peak detected at -0,61 V by 0,47 mA and 5,58 mA, respectively.It suggested a high electrocatalytic ability of the SS/G-OH electrode for the electrochemical oxidation reaction.The electrochemical process by the electrode could degrade >92% of the initial MB within 5 min and > 99% within 30 min.The GC data suggested that MB mainly degraded to CO2 and H2O.This graphene-based electrode could be a potential for the electrochemical oxidation of many organic pollutants to yield environmentally friendly products.

Graphene and its related compounds are among the emerging materials to be studied for many applications, especially for the electrochemical process. We prepared a stainless steel/hydroxyl functionalized graphene (SS/G-OH) electrode by anodic electrodeposition method. The G-OH dispersion is realized with a voltage of 30 V for electrodeposition variation time 1, 3, and 5 min with 316L stainless steel as an anode and cathode. The obtained SS/G-OH electrode was characterized by XRD, SEM-EDX, and FTIR. The G-OH modified SS electrode shows higher electrocatalytic ability than that of the bare SS electrode. The best electrodeposition time is 3 min. The electrochemical degradation of 20 ppm methyl orange (MO) by using the SS/G-OH electrode with an applied current of 1.5 A showed a concentration reduction of >99% after 30 min of reaction. The GC data suggest that MO was mainly degraded to CO2 and H2O. This graphene-based electrode could be of choice for the electrochemical degradation of industrial dyes.

A simple analyte separation through an in-situ volatilization system in a polytetrafluoroethylene (PTFE) container was carried out for boric acid analysis in a food product by spectrophotometry. Separation was conducted in two teflon containers divided into the reagents compartment (outer vessel) and sample compartment (inner vessel). System optimization was done by varying the curcumin content and ethanol: water ratio. The optimum condition of the volatilization system was achieved at a curcumin concentration of 0.1% and ethanol: water ratio of 3:1. LOD and LOQ measurements, respectively, gave a value of 0.0413 mg/L and 0.1088 mg/L. The established method was used to determine boric acid content in sausage products by UV-Vis Spectrophotometry at 555 nm. The boric acid concentration in food samples was found to be 0.913-3.518 mg/kg. The separating method through in-situ volatilization systems in a polytetrafluoroethylene (PTFE) container can be used for boric acid analysis in food samples.

Synthesis of silver nanoparticles (AgNPs) by use of well-tested reducing and capping agents has been studied widely to produce desired product qualities for many usages. However, the size, morphology, and stability of the colloidal AgNPs remain subject to intensive works. Here, we report on the stable EDTA capped AgNPs prepared by reducing Ag+ ions using ascorbic acid (AA) stabilized with ethylenediaminetetraacetate (EDTA) at mild conditions. The pH medium, the reducing and stabilizing agent concentrations, temperature, and reaction time were evaluated to give stable and monodispersed colloidal nanoparticles. The synthesis of colloidal AgNPs was successful at medium pH of 11 and a temperature of 30 degrees C. The peak of colloid localized surface plasmon resonance (LSPR) absorbance was observed at 396-398 nm, having a size distribution of about 17.9-23.8 nm, spherical shape, monodisperse, and zeta potential of -25.8 mV. The produced nanomaterials have good stability up to 24 weeks of storage time. The fabricated AgNPs show long-term stability, which is very promising for many potential applications.

The quartz crystal microbalance (QCM) modified by chitosan/α-pinene, prepared by spin-coating technique has been successfully developed with molecular imprinting polymer (MIP) concept. To remove the template, we carried out two treatments namely heating and vacuum in a desiccator. To find out selectivity of the sensor, the QCM modified with polymer chitosan has been tested with another analyte such as acetone, ethanol, N-amyl alcohol, iso-amyl alcohol. The result shows that chitosan/α-pinene coated QCM sensor can provide a good response as good as sensitivity. The best QCM at heating treatment in a furnace with the decline of frequency is 32 Hz, then the QCM vacuum pumping treatment with decline frequency is 27 Hz.

Analytical parameters including sensitivity in the QCM sensing system are critical to understand its sensing mechanism. We investigated the QCM analytical parameters after the QCM electrode surface was modified with polyvinyl acetate (PVAc) nanofiber for primary alcohols' vapor detection. The PVAc nanofibers were prepared by electrospinning method and were observed using a scanning electron microscope (SEM). The modified QCM sensing system was used to test the vapor of primary alcohols. The QCM sensitivity for methanol, ethanol, n-propanol, n-butanol, and n-pentanol was found to be 6.8 +/- 0.4, 13.1 +/- 0.5, 25.2 +/- 1.1, 39.7 +/- 1.9, and 51.9 +/- 2.6 Hz mg(-1) L, respectively. The limit of detection for npentanol vapor was 0.023 mg/L, which the highest of all. The shortest response time was 4s, when it was exposed to methanol vapor. The intermolecular interaction between the active surface and gaseous molecules is believed to responsible for frequency shift. The concentration of the analyte in the air is linearly correlated to the compound vapor pressure. The results could provide a new promising way to detect vapor of structurally similar of volatile organic compounds (VOCs) by QCM. (C) 2019 Elsevier B.V. All rights reserved.