A pilot-scale hybrid constructed wetland with vertical flow and horizontal flow in series was constructed and used to investigate organic material and nutrient removal rate constants for wastewater treatment and establish a practical predictive model for use. For this purpose, the performance of multiple parameters was statistically evaluated during the process and predictive models were suggested. The measurement of the kinetic rate constant was based on the use of the first-order derivation and Monod kinetic derivation (Monod) paired with a plug flow reactor (PFR) and a continuously stirred tank reactor (CSTR). Both the Lindeman, Merenda, and Gold (LMG) analysis and Bayesian model averaging (BMA) method were employed for identifying the relative importance of variables and their optimal multiple regression (MR). The results showed that the first-order–PFR (M2) model did not fit the data (P > 0.05, and R2 < 0.5), whereas the first-order–CSTR (M1) model for the chemical oxygen demand (CODCr) and Monod–CSTR (M3) model for the CODCr and ammonium nitrogen (NH4−N) showed a high correlation with the experimental data (R2 > 0.5). The pollutant removal rates in the case of M1 were 0.19 m/d (CODCr) and those for M3 were 25.2 g/m2∙d for CODCr and 2.63 g/m2∙d for NH4-N. By applying a multi-variable linear regression method, the optimal empirical models were established for predicting the final effluent concentration of five days' biochemical oxygen demand (BOD5) and NH4-N. In general, the hydraulic loading rate was considered an important variable having a high value of relative importance, which appeared in all the optimal predictive models.
In article number 1801854, Sang Yoon Park, Soo‐Jin Park, Le Hoang Sinh, Min Kyoon Shin, and co‐workers demonstrate a simple and scalable method to fabricate a paper‐based yarn‐type supercapacitor from twisting reduced graphene oxide (rGO) and single walled carbon nanotubes (SWNTs)‐coated Korean traditional paper (KTP). The yarn‐type rGO/SWNT@KTP supercapacitor shows excellent electrochemical performance and long‐life operation.
In this study, a new method for preparation of cross-linked magnetic chitosan particles (MCPs) from steel slag and shrimp shells using green tea extract as crosslinking reagent has been presented. The MCPs obtained were characterized by means of X-ray diffraction analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy and magnetic properties, and then were used to investigate the adsorption properties of Cu(II) and Ni(II) ions in aqueous solutions. The influence of experimental conditions such as contact time, pH value, adsorbent dose and initial metal concentration, and the possibility of regeneration were studied systematically. The Cu(II) and Ni(II) adsorption isotherms, kinetics and thermodynamics have been measured and discussed. The results show that the synthesized MCPs have high adsorption capacity for both metal ions (126.58 mg/g for Cu(II) and 66.23 mg/g for Ni(II)), and have excellent regeneration stability with efficiency of greater than 83% after five cycles of the adsorption–regeneration process. The adsorption process of Ni(II) and Cu(II) on MCPs was feasible, spontaneous and exothermic, and better described by the Langmuir model and pseudo-second-order kinetic equation. The MCPs can be applied as a low cost and highly efficient adsorbent for removal of heavy metals from wastewater due to its high adsorption capacity, easy recovery and good reusability.
Fiber‐based sensors integrated on textiles or clothing systems are required for the next generation of wearable electronic platforms. Fiber‐based physical sensors are developed, but the development of fiber‐based temperature sensors is still limited. Herein, a new approach to develop wearable temperature sensors that use freestanding single reduction graphene oxide (rGO) fiber is proposed. A freestanding and wearable temperature‐responsive rGO fiber with tunable thermal index is obtained using simple wet spinning and a controlled graphene oxide reduction time. The freestanding fiber‐based temperature sensor shows high responsivity, fast response time (7 s), and good recovery time (20 s) to temperature. It also maintains its response under an applied mechanical deformation. The fiber device fabricated by means of a simple process is easily integrated into fabric such as socks or undershirts and can be worn by a person to monitor the temperature of the environment and skin temperature without interference during movement and various activities. These results demonstrate that the freestanding fiber‐based temperature sensor has great potential for fiber‐based wearable electronic platforms. It is also promising for applications in healthcare and biomedical monitoring.
In this study, a novel magnetic hydroxyapatite/chitosan composite (HA/Fe3O4/CS) prepared from steel slag, shrimp shells, and bovine bones, and then cross-linked with a green tea extract was used as an adsorbent for Ni(II) ion removal from aqueous solution. Various techniques (SEM, FTIR, XRD, VSM) were used to characterize the adsorbent. Batch experiments were conducted to investigate the adsorption properties of Ni(II) ions on HA/Fe3O4/CS. The optimum conditions for the adsorption process were studied in detail. The adsorption isotherm, mechanism, kinetics, and thermodynamics were further discussed. Besides, the desorption and reusability of the adsorbent were evaluated for further applications. The results indicated that the HA/Fe3O4/CS composite has the potential application for removal of Ni(II) ions from aqueous solution with a maximum adsorption capacity of 112.36 mg/g at optimal conditions (pH of 6, contact time of 60 min, room temperature, and adsorbent dose of 3 g/L). The adsorption process of Ni(II) on HA/Fe3O4/CS was feasible, spontaneous, exothermic, and more favorable at lower temperature. Adsorption isotherm and kinetics were suitable to be described by the Langmuir model and pseudo-second-order kinetic equation, respectively. Recycling results confirmed that the HA/Fe3O4/CS composite maintains a great reusability potential for five consecutive cycles with Ni(II) removal efficiency of greater than 85%. The adsorbent can be easily regenerated by using HCl and EDTA solutions. The overall study revealed that the magnetic hydroxyapatite/chitosan composite can be applied as a low cost, environmental friendly, and highly efficient adsorbent for removal of Ni(II) ions from wastewater because of its high adsorption capacity, easy recovery, and good reusability.
A simple and scalable method to fabricate a yarn‐type supercapacitor with a large specific capacitance without the aid of traditional pseudocapacitive electrode materials such as conducting polymers and metal oxides is reported. The yarn‐type supercapacitors are made from twisting reduced graphene oxide (rGO) or/and single‐walled carbon nanotubes (SWNTs)‐coated Korean traditional paper (KTP). The yarn‐type paper supercapacitor displays surprisingly enhanced electrochemical capacitance values, showing synergistic effect between rGO and SWNTs (500 times larger than performance of yarn‐type rGO‐coated paper supercapacitors). Coating rGO or/and SWNTs on KTP gives good morphology to the composite film, in which porosity increases and mean pore diameter decreases. The yarn‐type rGO/SWNT paper supercapacitor shows good mechanical strength, high flexibility, excellent electrochemical performance, and long‐life operation. The yarn‐type supercapacitor has an excellent electrochemical performance with a specific capacitance of 366 F g−1 at scan rate of 25 mV s−1 and high stability without any degradation in electrical performance up to 10 000 charge–discharge cycles. The average capacitance of rGO/SWNT@KTP yarn‐type supercapacitors is seven times higher than that of sheet‐type supercapacitors at scan rate of 500 mV s−1. The lighting of a red light‐emitting diode (LED) is demonstrated by the yarn‐type paper supercapacitor without connecting supercapacitors in series.
The development of low cost, portable diagnostic tools for in-field detection of viruses and other pathogenic microorganisms is in great demand but remains challenging. In this study, a novel approach based on reduced graphene oxide-polyaniline (rGO-PANi) film for the in situ detection of loop-mediated-isothermal-amplification (LAMP) products by means of open circuit potential measurement is proposed. The pH-sensitive conducting polymer PANi was electro-deposited onto rGO coated screen printed electrodes and tuned to be at the emeraldine state at which the pH sensitivity was maximized. By combining PANi and rGO, the pH sensitivity of the system was modulated up to about −64 mV per pH unit. This enabled the number of amplified amplicons resulting from the isothermal amplification process to be monitored. The sensor was then examined for monitoring LAMP reactions using Hepatitis B virus (HBV) as a model. This simple, low-cost, reproducible and sensitive interfacing layer is expected to provide a new possibility for designing point-of-care sensors under limited-resource conditions.
In this study, the epoxidized soybean oil (ESO) was successfully synthesized from soybean oil based on its double bond, and used to synthesize the ESO-modified phenolic resin via reaction between ESO, phenol and formaldehyde. The ESO contents used in this study vary in range from 0 to 40 wt%. Then, the obtained ESO modified phenolic resin (ESO-PR) was used as resin matrices to fabricate glass-fiber-based composites by using prepreg technique. The chemical structures of both epoxidized soybean oil and phenolic resin modified with epoxidized soybean oil were confirmed with the help of Fourier transform infrared spectrometry (FTIR). The mechanical characteristics of fabricated composite materials examined include the tensile property, flexural property, impact property as well as the mode I interlaminar fracture toughness, while the morphology composite materials were also confirmed by scanning electron microscopy. The test results showed that at 20 wt% of ESO-PR, the mode I interlaminar fracture toughness for both propagation and initiation, the tensile strength, flexural strength and impact strength were increased by 78.3 and 84.5%, 7.0%; 20.5 and 39.7%, respectively. The scanning electron microscopy (SEM) observation indicated that the fracture surface of the modified composite was rougher when compared to the fracture surface of the pristine composite, and hence more energy was needed for the crack to propagate.
Bio-based bacterial cellulose (BC) epoxy composites were manufactured and their mechanical properties were examined. The BC was initially fabricated from Vietnamese nata de coco by means of alkaline pretreatment followed by solvent exchange. The obtained fibers were dispersed in epoxy resin (EP) by both mechanical stirring and ultrasonic techniques. The resulting blend was used as the matrix for glass-fiber (GF) composite fabrication using a prepreg method followed by multiple hot-press-curing steps. The morphology, mechanical characteristics and mode-I interlaminar fracture toughness of the fabricated composites were investigated. With a 0.3-wt% BC content, the mode-I interlaminar fracture toughness for both crack initiation and crack propagation were improved by 128.8% and 1110%, respectively. The fatigue life was dramatically extended by a factor of 12, relative to the unmodified composite. Scanning electron microscopy images revealed that the BC plays a vital role in increasing the interlaminar fracture toughness of a GF/EP composite via the mechanisms of crack reflection, debonding and fiber-bridging.
Using bacterial cellulose (BC) prepared from Vietnamese nata-de-coco via an alkaline pre-treatment followed by a solvent exchange process, epoxy resin (EP)/BC biocomposites were fabricated using three different dispersion techniques: mechanical stirring only, both mechanical stirring and grinding, and both mechanical stirring and ultrasonication. The surface of BC was modified with a silane coupling agent to improve the chemical affinity between BC and epoxy resin. The biocomposite materials comprising BC, epoxy resin, and methylhexahydrophthalic anhydride as a curing agent were obtained from hot curing processing. The morphology and mechanical properties such as fracture toughness, enhanced K IC values, and tensile and flexural properties of the bio-based composites were compared with those of the virgin epoxy resin. The silane coupling agent had a vital role in improving the mechanical characteristics of the bio-based composites. For instance, K IC values, tensile strength, Young’s modulus, and flexural strength of the 0.3 wt% BC/epoxy composites with the presence of 2.0 wt% silane coupling agent were 0.7740 MPa m1/2, 53.32 MPa, 1.68 GPa, and 83.05 MPa. These values represent improvements of 36.77, 17, 15.86, and 14.42%, respectively, compared to a neat epoxy resin. Scanning electron microscopy revealed the rough fracture surface of epoxy resin/BC-based biocomposites with a multipathway crack, requiring more energy before breakage.
The waste produced by bamboo stick production processing was collected from a Vietnamese craft village and used as a source of microfibril cellulose (MFC) for a filler of unsaturated polyester (UP) resin based composites in this study. A mixture of MFC in UP was obtained by directly introducing the bamboo pulp into UP resin followed by a grinding process using a ball-grinding machine. A master batch method was also adopted for composite preparation, in which a high-content solution of MFC in UP resin was first fabricated and then diluted to prepare another solution with the desired content. Morphology and mechanical characteristics of UP resin based composites were investigated. Effect of different methods of preparation, such as hand lay-up and vacuum bagging methods, on the mechanical properties of glass fiber reinforced UP resin composites was also examined, showing that the tensile strength of composite materials with 0.3 wt% MFC was increased by 10.24% (for the hand lay-up method) and 19.62% (for the vacuum bagging method) when compared with the pristine composite material. The flexural strength increased from 192.40 MPa to 208.63 MPa and the impact strength increased by 19.6% from 158.28 kJ/m2 to 186.84 kJ/m2 for the hand lay-up method.
The major requirements for accelerating the process of anaerobic digestion and energy production are breaking the structure of waste activated sludge (WAS), and transforming it into a soluble form suitable for biodegradation. This work investigated and analysed a novel bench-scale ultrasonic system for WAS disruption and hydrolysis using ultrasonic homogenization. Different commercial sonoreactors were used at low frequencies under a variety of operating conditions (intensity, density, power, sonication time, and total suspended solids) to evaluate the effects of the equipment on sludge hydrolysis and to generate new insights into the empirical models and mechanisms applicable to the real-world processing of wastewater sludge. A relationship was established between the operating parameters and the experimental data. Results indicated an increase in sonication time or ultrasonic intensity correlated with improved sludge hydrolysis rates, sludge temperature, and reduction rate of volatile solids (33.51%). It also emerged that ultrasonication could effectively accelerate WAS hydrolysis to achieve disintegration within 5–10 min, depending on the ultrasonic intensity. This study also determined multiple alternative parameters to increase the efficiency of sludge treatment and organic matter reduction, and establish the practicality of applying ultrasonics to wastewater sludge pretreatment.
Using bacterial cellulose (BC) prepared from Vietnamese nata-de-coco via an alkaline pre-treatment followed by a solvent exchange process, epoxy resin (EP)/BC biocomposites were fabricated using three different dispersion techniques: mechanical stirring only, both mechanical stirring and grinding, and both mechanical stirring and ultrasonication. The surface of BC was modified with a silane coupling agent to improve the chemical affinity between BC and epoxy resin. The biocomposite materials comprising BC, epoxy resin, and methylhexahydrophthalic anhydride as a curing agent were obtained from hot curing processing. The morphology and mechanical properties such as fracture toughness, enhanced K values, and tensile and flexural properties of the bio-based composites were compared with those of the virgin epoxy resin. The silane coupling agent had a vital role in improving the mechanical characteristics of the bio-based composites. For instance, K IC values, tensile strength, Young’s modulus, and flexural strength of the 0.3 wt% BC/epoxy composites with the presence of 2.0 wt% silane coupling agent were 0.7740 MPa m -1/2 , 53.32 MPa, 1.68 GPa, and 83.05 MPa. These values represent improvements of 36.77, 17, 15.86, and 14.42%, respectively, compared to a neat epoxy resin. Scanning electron microscopy revealed the rough fracture surface of epoxy resin/BC-based biocomposites with a multipathway crack, requiring more energy before breakage.
As a green filler comprising both nano and micro-sized fibrils, micro/nano white bamboo fibrils (MWBFs) were treated with a silane coupling agent (S-MWBFs) prior to their introduction in an epoxy resin (EP). The sequential processes of steam explosion, alkaline treatment, and micro grinding were used to prepare to MWBFs. The effects of the S-MWBFs on various characteristics of the cured EP such as compatibility, fracture toughness, morphology, mechanical property, and flame retardation were studied. The fracture toughness and mechanical characteristics of both the storage modulus and tand maximum increased following addition of the S-MWBFs to the EP. Notably, the fracture toughness of the EP with 0.3 wt% of S-MWBFs was 22.2% higher than that of unmodified resin. Scanning electron microscopy presented somewhat rougher surfaces with shear deformation and tortuously twisting cracks, resulting in a higher fracture toughness in S-MWBFmodified epoxy samples. However, fire testing showed that the presence of S-MWBFs increased the burning rate of the EP.
In this study, Pt nanoparticles are deposited on the surface of nitrogen-sulfur functionalized reduced graphene oxide and mixed with double wall carbon nanotubes (Pt/NS-rGO/DWCNT). The obtained nanocomposite is used as an electrocatalyst for the ethanol electro-oxidation reaction (EOR). CO oxidation studies with differential electrochemical mass spectroscopy (DEMS) show a lower onset potential indicating higher poisoning tolerance of these materials. The electrocatalytic activity of the Pt/NS-rGO/DWCNT nanocomposite is studied at different temperatures (40, 50, 60, and 70 °C) and compared with that of Pt/rGO, Pt/rGO/DWCNT composites and commercial carbon-supported Pt catalyst. Pt/rGO/DWCNT and Pt/NS-rGO/DWCNT display significantly higher ethanol electro-oxidation currents especially at low potentials relevant to fuel cell applications. At high temperatures (>50 °C), Pt/NS-rGO/DWCNT is the most active catalyst in concordance with its higher apparent activation energy. Pt/NS-rGO/DWCNT is also the most durable of the catalysts after a 500 potential cycle test and suffers the least from poisoning effects during chronopotentiometric testing. These results allow to conclude that combining NS-functionalized graphene catalyst support with DWCNT to form a composite provides excellent performances due to enhanced Pt electrocatalytic activity from NS-functionalization and enhanced mass transfer from the DWCNT filler.
