Metal oxide-modified biochar showed excellent adsorption performance in wastewater treatment. Iron nitrate and potassium permanganate were oxidative modifiers through which oxygen-containing groups ...and iron–manganese oxides could be introduced into biochar. In this study, iron–manganese (Fe–Mn) oxide-modified biochar (BC-FM) was synthesized using rice straw biochar, and the adsorption process, removal effect, and the mechanism of cadmium (Cd) adsorption on BC-FM in wastewater treatment were explored through batch adsorption experiments and characterization (SEM, BET, FTIR, XRD, and XPS). Adsorption kinetics showed that the maximum adsorption capacity of BC-FM for Cd(II) was 120.77 mg/g at 298 K, which was approximately 1.5–10 times the amount of adsorption capacity for Cd(II) by potassium-modified or manganese-modified biochar as mentioned in the literature. The Cd(II) adsorption of BC-FM was well fit by the pseudo-second-order adsorption and Langmuir models, and it was a spontaneous and endothermic process. Adsorption was mainly controlled via a chemical adsorption mechanism. Moreover, BC-FM could maintain a Cd removal rate of approximately 50% even when reused three times. Cd(II) capture by BC-FM was facilitated by coprecipitation, surface complexation, electrostatic attraction, and cation-π interaction. Additionally, the loaded Fe–Mn oxides also played an important role in the removal of Cd(II) by redox reaction and ion exchange in BC-FM. The results suggested that BC-FM could be used as an efficient adsorbent for treating Cd-contaminated wastewater.
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•A highly adsorptive Fe–Mn oxide-modified biochar was prepared using Fe(NO)3 and KMnO4.•The form and valence of Fe2O3 and Mn2O3 in BC-FM changed during Cd(II) adsorption.•BC-FM showed high removal capacity even reused three times (45.4%–66.2%).•Cu and Zn inhibited Cd(II) adsorption by competing for adsorption sites.
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•The effects of three bioleaching methods for extracting rare earth elements from ion-adsorption type rare earth ore were compared.•Rare earth ores had certain toxic effects on ...Aspergillus niger strain.•Organic acids produced by the strain have good acidolysis and complexation for leaching.•The strain and rare earth ore before and after leaching were analyzed by various characterization methods.
Rare earth elements (REEs) are essential elements in many technology industries. The commonly used ammonium salt method has caused a bad impact on environment. Bioleaching is widely recognized as a low energy, relatively simple and environmentally friendly method. The purpose of this work is to extract REEs from ion-adsorption type rare earth ore by using three different bioleaching methods (one-step, two-step, and spent medium method, respectively) and the strain used was Aspergillus niger strain. Major organic acids produced during microbial growth were detected and the REEs leaching efficiency of three methods was compared. In addition, the interaction between the strain and their metabolites and rare earth ore was investigated by FT-IR, XRD, SEM-EDS, and TEM-EDS during the leaching process. In the end, it was found that the spent medium method had the best leaching effect, and various characterization methods showed that the three bioleaching methods had obvious changes before and after leaching, among which the spent medium method had the most significant effect. Additionally, through the analysis, it can be concluded that the complexation and acidolysis may occur in the bioleaching process.
•The IE of Cu in HCl solution with 200 mg/L of Ce-10% inhibitor was up to 98%.•The icorr of Cu in 200 mg/L of Ce-10% solution was dropped 2 orders of magnitude.•The adsorption/passivation film in ...metal/solution interface were deeply analyzed.
Background: A new high-effectively corrosion inhibitor was used to replace the traditional corrosion inhibitor and reduce the environment pollution.
Methods: Through hydrothermal synthesis, Ce and N co-doped carbon dots (Ce@N-CDs) were generated. Before the performance characterization, the microstructure and chemical composition of Ce@N-CDs were firstly investigated by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) techniques. The electrochemical test revealed that the IE of Ce-10% (200 mg/L) on copper was as high as 98%, presenting the best inhibition effect. According to the adsorption isotherm analysis, the Ce@N-CDs mainly adsorbed according to the Langmuir model, and the adsorption process was completed by combining physical and chemical adsorption.
Significant findings: Through the morphology, energy dispersive spectrometer (EDS) and XPS analysis of copper surface after corrosion process, it was found that the Ce@N-CDs formed a dense adsorption/passivation film on the copper surface. The adsorption film mainly came from the pairing of unsaturated bonds between N-doped CDs (N-CDs) and copper surface. The passivation film mainly came from the oxide formed by the reaction between Ce and the surrounding environment. Their dense structure could effectively inhibit the infiltration and erosion of corrosive medium.
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Properties of explosion suppression material have a significant impact on controlling the explosion propagations. Bentonite, with a large surface area and abundant pore structure, can adsorb free ...radicals during the explosion reactions. It is a kind of ideal explosion suppression materials. However, bentonite can easily absorb moisture and solidify into cakes in a humid environment, which lacks the possibilities of reactions with radicals in explosions and results in a poor suppression effect. To enhance the space suspension property of bentonite, in this paper, three surface modification methods are proposed to prepare the modified bentonite-based powder by using a silane coupling agent modification, silica encapsulation modification, and quaternary ammonium salt insertion modification. Then, changes in the characteristics of modified bentonite are analyzed and characterized using FTIR, SEM, et al. The results show that the pore structures fundamentally changed and surface is poor combination with water, which greatly solves the “Caking” problem.
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•Modified powders maintain excellent explosion suppression in wet environments.•Surface modification, encapsulation modification, insertion modification.•Characterization: particle size, infrared, morphology, DSC-TGA, etc.•Mechanism: inhibition of explosion in the free radical evolution characterization.
Macroalgae contains micro and macromolecules of great interest for various sectors, for example, food, cosmetics, and pharmaceuticals. These compounds can be obtained through different extraction ...methods, among them the use of organic solvents with varying polarities. In this study, materials were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy, infrared spectrometry, X-ray diffraction and differential scanning calorimetry in the seaweed biomasses before and after an extraction process with organic solvents. The red macroalgae Crassiphycus birdiae, cultivated on the northeast coast of Brazil, appeared, after extraction, as an amorphous material with some porosity. Its composition includes the elements carbon, oxygen, sodium, magnesium, sulfur, chlorine, potassium, aluminum, silicon, calcium, and iron. The presence of the agar polysaccharide was also verified by infrared spectroscopy. The decomposition of this polysaccharide was observed using differential scanning calorimetry.
A start-up study of lab-scale up-flow anaerobic sludge blanket fixed-film reactor (UASFF) was conducted to produce biohydrogen from palm oil mill effluent (POME). The reactor was fed with POME at ...different hydraulic retention time (HRT) and organic loading rate (OLR) to obtain the optimum fermentation time for maximum hydrogen yield (HY). The results showed the HY, volumetric hydrogen production rate (VHPR), and COD removal of 0.5–1.1 L H2/g CODconsumed, 1.98–4.1 L H2 L−1 day−1, and 33.4–38.5%, respectively. The characteristic study on POME particles was analyzed by particle size distribution (PSD), Scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDX). The microbial Shannon and Simpson diversity indices and Principal Component Analysis assessed the alpha and beta diversity, respectively. The results indicated the change of bacterial community diversity over the operation, in which Clostridium sensu stricto 1 and Lactobacillus species were contributed to hydrogen fermentation.
•Fermentative hydrogen production from palm oil mill effluent.•Substrate particle size, surface morphology, elemental identification were studied.•Maximum H2 production at HRT 8 h/OLR 45.4 g COD L−1 day−1.•Evolution in microbial community before and after dark fermentation.•Clostridium sensu stricto 1 mostly contributed to biohydrogen production.
Cathode recirculation provides a new solution to the accelerated degradation of proton exchange membrane fuel cells (PEMFCs) due to low humidity and high potential at low load conditions. Analyzing ...the internal impact mechanisms is basis for a more appropriate use of this technology. This paper presents a systematic investigation of the mechanisms by which key operating parameters of the cathode recirculation, including current density, cathode recirculation ratio, and stoichiometry of the fresh air path, affect the internal and external properties of PEMFCs. The voltage suppression effect and humidification effect under different cathode recirculation strategies are first analyzed. Then, as a novelty, the distribution of relaxation times (DRT) method is used to deconvolve electrochemical impedance spectra and qualitatively resolve the polarization impedance under different strategies. DRT is enabled to separate up to five polarization processes with different time constants and assign them to oxygen diffusion, oxygen reduction reaction and proton transport processes affected by the cathode recirculation. Finally, DRT quantified the change in ohmic impedance due to cathode recirculation and confirmed the effect of external humidity changes. This work provides a more in-depth insight into internal mechanisms of cathode recirculation in PEMFCs, and especially provides a comprehensive theoretical basis for the development of idle controllers for automotive PEMFCs in terms of improved durability.
•A systematic study of cathode recirculation on PEMFC under low-load conditions.•The polarization process at various recirculation strategies are identified by DRT.•Cathode circulation has positive prospects in vehicle self-humidifying PEMFC system.
The deformation behavior and microstructure characteristics of laser-welded Ti-6Al-4V titanium alloy joints under variable amplitude fatigue ranging from 320 to 380 MPa (initial maximum stress) were ...investigated in steps of 10 MPa. Each fatigue test included three different stages: the maximum stress amplitude was initial one for the first stage, but increased by 1.2 and 1.4 times for the second and third stages, respectively. The results showed that the variable amplitude fatigue limit of laser-welded the Ti-6Al-4V joint was 339 ± 5 MPa. Fractography analysis revealed that the fatigue cracks originated from the surface in the weld metal (WM) and were caused by the differences of grain size and texture orientation between WM and heat-affected zone. The average grain size of WM was significantly larger than that of other regions. Acicular α’ martensite was distributed mainly in the coarse grains of WM and its orientation was more concentrated, leading to the preferred orientation. Furthermore, the accumulation of dislocations on the acicular α’ and β phase interface led to fatigue crack initiation owing to stress concentration. In addition, the lager average Schmid factor and smaller deviation in WM of the joint at a large stress amplitude was owing to the smaller relative geometrical orientation.
•The variable amplitude fatigue behavior of laser-welded Ti-6Al-4V joint was studied.•Differences in grain size and orientation lead to joint fracture in weld metal.•Dislocations accumulated on the phase interface are key elements leading fracture.•The characteristics of joint microstructure and fracture behavior are related.
During the industrial processing of agricultural products, the steps to be followed are more numerous and lead to the appearance of a varied range of waste, a source of pollution in the environment. ...However, this waste is an important source of energy for ruminants, which greatly benefit from it. This work is an experimental and thermodynamic study of the solar drying of apple and orange waste. In this work, we present a new approach for the thermodynamics study of drying apple and orange waste, as well as the evaluation of this waste as a complement in the feeding of ruminants. This evaluation has led to the study of the properties of four powders obtained by drying apple and orange waste with two methods, namely thin-film drying under the sun, and thin-film drying in the greenhouse solar dryer. Several experiments were carried out on the powders obtained, to study the effect of drying on their physical, physicochemical, microbiological, and microscopic properties. The goal is to know and determine the optimal drying method that provides us with dry, healthy, nutritious, and better quality food waste to be included in ruminant rations. According to the obtained results from this comparative study, it was found that the waste dried inside the greenhouse dryer is of better quality. The thermodynamic parameters derived from the proposed new approach are discussed and compared with literature results. The negative values of Gibbs free energy indicate that solar drying of apple and orange waste is a spontaneous process.
•Apple and orange waste were dried in greenhouse and in the open air.•Solar drying is a necessary intermediate step in the treatment of agro-food waste.•Dried apple and orange waste obtained are of appreciable nutritional quality.•A new thermodynamic approach was evaluated and compared with literature results.•In the present study conditions, it was found that the drying process is spontaneous.
In the present paper, graphitic carbon nitride (g-C3N4) was prepared using a conventional hydrothermal process. Several characterization methods were applied to analyze the resulting g-C3N4 sample, ...such as: X-ray diffraction (XRD), ultraviolet-visible (UV–Vis) spectrophotometry, attenuated total reflectance -Fourier-transform infrared (ATR-FTIR) spectroscopy and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). The pollutant selected to measure the g-C3N4 photocatalytic performance was methylene blue (MB). Using Response Surface Methodology (RSM), the pH solution effects, photocatalyst dose (mg/L), and irradiation period (min) were examined and adjusted. The optimal conditions, which included 1.3 g/L of g-C3N4 photocatalyst, solution pH = 10.83, and irradiation time = 119.3 min, resulted in a degradation efficiency of 86.58 %. The principal active species involved in photocatalytic degradation have been identified and a potential mechanism has also been provided. Additionally, the degradation kinetics were monitored and obtained to follow pseudo-second order kinetics.
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•g-C3N4 was synthesized successfully using a conventional hydrothermal method and characterized by different techniques.•The synthesized photocatalyst was used for the photocatalytic degradation of the organic pollutant MB.•The photocatalytic process was accompanied by RSM to optimize the factors using BBD theory.•The main active species involved in photocatalytic degradation were identified; a potential mechanism was proposed.
