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A dynamic model of a flexible rotor supported by ball bearings with rubber damping rings was proposed by combining the finite element and the mass-centralized method. In the proposed model, the rotor was built with the Timoshenko beam element, while the supports and bearing outer rings were modelled by the mass-centralized method. Meanwhile, the influences of the rotor’s gravity, unbalanced force and nonlinear bearing force were considered. The governing equations were solved by precise integration and the Runge-Kutta hybrid numerical algorithm. To verify the correctness of the modelling method, theoretical and experimental analysis is carried out by a rotor-bearing test platform, where the error rate between the theoretical and experimental studies is less than 10%. Besides that, the influence of the rubber damping ring on the dynamic properties of the rotor-bearing coupling system is also analyzed. The conclusions obtained are in agreement with the real-world deployment. On this basis, the bifurcation and chaos behaviors of the coupling system were carried out with rotational speed and rubber damping ring’s stiffness. The results reveal that as rotational speed increases, the system enters into chaos by routes of crisis, quasi-periodic and intermittent bifurcation. However, the paths of crisis, quasi-periodic bifurcation, and Hopf bifurcation to chaos were detected under the parameter of rubber damping ring’s stiffness. Additionally, the bearing gap affects the rotor system’s dynamic characteristics. Moreover, the excessive bearing gap will make the system’s periodic motion change into chaos, and the rubber damping ring’s stiffness has a substantial impact on the system motion.

This study aims to take the compound planetary gear train as an example to investigate how the vibration isolator affects the dynamic characteristics of the gear system. The dynamic parameters are obtained from the finite element model of the gearbox case with the vibration isolators by the substructure method. The lumped mass method is used to construct the systematic coupled dynamic model of the compound planetary gear train with the marine twin-layer gearbox case. The dynamic response of the coupled system is calculated by the numerical calculation method of the Fourier series. The number of vibration isolators negatively affects the bearing forces of the input shaft, output shaft, and planets. The influence of the number of vibration isolators on LSCs is different in the differential stage and the encased stage. When the vibration isolators stiffness is less than 200 N/μm, the stiffness of the vibration isolator has a significant effect on the bearing forces of the input shaft, output shaft, and planets. The increase in the stiffness of the vibration isolator would increase the LSCs of the differential stage and decrease the LSCs of the encased stage. The number and stiffness of the vibration isolator have influences on the bearing forces and the LSCs. Compared with the LSCs in the differential stage, the LSCs in the encased stage are more sensitive to the number and stiffness of vibration isolators.

The helicopter tail drive shaft system is a typical multi-point supported drive shaft system, with a long span that can lead to serious vibration problems. Shaft vibration can be effectively reduced by installing a rubber-silicone oil combined damper between the bearing and bearing pedestal at the support point along the tail drive shaft. Stiffness and damping characteristics of the rubber-silicone oil combined damper are important factors affecting shaft vibration. In this study, the effects of silicone oil on the stiffness and damping of rubber-silicone oil combined damper were analyzed through simulations. The simulation method was experimentally verified and factors influencing the static stiffness, dynamic stiffness, and damping characteristics of the damper were investigated. In addition, the influence of damper dimensions and external excitation frequency on the stiffness and loss factor of the damping ring in the presence and absence of silicone oil were examined. The presence of silicone oil increases the difference between the dynamic stiffness and the loss factor. As the viscosity of the silicone oil increases, the static stiffness, dynamic stiffness, and loss factor of rubber-silicone oil combined dampers increase. The results have important guiding significance in the design of dampers for shafting systems.

As one of the hard-templating methods, MgO-templating was employed to recycle cotton to produce activated carbon with magnesium acetate as MgO precursor. Results showed that cotton carbonized while magnesium acetate decomposed to nanoscale MgO particles based on thermogravimetric and X-ray diffraction analysis. Carbonized residuals of cotton were able to replicate the MgO morphology thus creating pores. The size of MgO varied with impregnation ratio, treatment temperature, and time. Overall, the optimum conditions were MgO/cotton impregnation ratio 0.25, temperature 800 °C, and treatment time 60 min. Cotton-based activated carbon thus produced manifested surface area and total pore volume of 1139 m2/g and 0.85 cm3/g respectively. Both micropores and mesopores were detected based on iodine, methylene blue adsorption values, and N2 adsorption-desorption studies.

The feasibility of preparing activated carbon by chemical activation from textile waste flax was studied. According to thermogravimetric analysis, H3PO4 and ZnCl2 changed the pyrolysis behavior of flax. Reactions between H3PO4 or ZnCl2 degradation intermediaries and flax resulted in flax carbonization and activation. The effects of activation temperature, time and impregnation ratio on yield, micropore, mesopore and elemental composition were discussed in detail. Results showed that the optimum activation temperature was 700 °C for H3PO4 and 800 °C for ZnCl2 while optimum activation time and impregnation ratio for both were 60 min and 1.0. H3PO4 activation was higher in yield while ZnCl2 activation obtained carbons that were higher both in surface area and mesopore volume. H3PO4 and ZnCl2 were able to carbonize the original flax components and produced activated flax that is highly carbonaceous, rich in surface functional groups and powdered in particle size.

As one of the hard templating method for making porous materials, MgO templating was under intensive investigation for its various advantages. In this research, MgO templating was employed to reuse textile waste cotton. The main purpose was to compare the pyrolysis behaviors of four MgO-precursors (magenesium acetate, magnesium chloride, magnesium citrate and MgO particles) for their effectiveness as templating agents. Thermogravimetric and X-ray diffraction analysis showed that precursors decomposed stepwise or disintegrate to form nano-size MgO particles. At the same time, carbonized cotton was able to replicate the morphology of MgO particles to create porous structures. The effects of precursor and treatment temperature on the morphology of MgO, pore structures and surface chemistry were investigated. Results proved that by manipulating templating conditions, cotton waste was able to produce activated carbon of various properties.

Different inorganic iron salts were selected as activating agents to investigate the effects of chloridion (Cl−) and iron in different valence states (Fe3+ and Fe2+) on pore and structure development of polyester fabric wastes-based activated carbons. Physicochemical properties of activated carbons were conducted by EA, N2 adsorption/desorption isotherms, XRD, SEM, XPS and FTIR. And the pyrolysis characteristics of the samples were detected by TG analysis. The results showed that carbons activated by FeCl3 and FeCl2 had well-developed porosity with BET surface areas around 1400 m2/g, almost 3.7 times larger than that by FeSO4, which was attributed to the formation of C Cl bond, facilitating to motivate the cross-linking reaction. The diversity in microporosity was found between carbons activated by FeCl3 and FeCl2 on account of the different roles of Fe3+ and Fe2+ and the distinct pyrolysis pathway. Furthermore, carbon activated by FeCl2 presented excellent adsorption performance toward eriochrome black T with the maximum adsorption capacity of 450.23 mg g−1.

FeCl3/ZnCl2 was used as activating agent in order to prepare cotton waste-based activated carbon. The optimal conditions for activated carbon determined by orthogonal experiments were as follows: activation temperature of 400 °C, mass ratio of 1:1 (FeCl3/ZnCl2), and activation time of 1 h. Thermogravimetric analysis was conducted to investigate the weight loss process. N2 adsorption/desorption isotherms, XRD, SEM, and FTIR were provided to analyze the crystal structure, pore development, morphological structure, and surface chemistry, respectively. The possible pore development was ascribed to the formation of molten ZnCl2 and Fe-species, which then act as templates inside the carbon to form pore structures. This process was also related to dehydration of ZnCl2 and FeCl3 on cotton waste. Carbon activated by FeCl3/ZnCl2 exhibited higher BET surface area (1342 m2 g−1) than carbon activated using FeCl3 (504 m2 g−1). The adsorption performance of activated carbon was estimated using methylene blue and eriochrome black T.

Taking the marine encased differential gear train as an example, the relationship between the journal bearing parameters and the meshing force of the transmission system is analyzed. In this paper, the dynamic model of the encased differential gear train with journal bearing is established considering the factors of time-varying meshing stiffness and comprehensive transmission error. In this dynamic model, four stiffnesses and four damping coefficients are applied to characterize the asymmetry and interaction of the oil film stiffness and damping of planet bearing. The system responses are calculated by the Fourier series numerical algorithm. The results show that the introduction of journal bearing in encased differential gear train can contribute to gearbox vibration reduction. Moreover, the planet bearing parameters (e.g., clearance-to-radius ratio and eccentricity ratio) of the differential stage affect the meshing forces of both the differential and encased stages. In addition, the influence of the planet bearing parameters of the encased stage on the meshing force of the encased stage is more obvious than that of the differential stage. This work may develop a theoretical analysis framework for the design and manufacture of marine transmission systems in the future.

Textile waste jute was activated by H3PO4 and ZnCl2 for reuse as activated carbon. Thermal degradation behavior of jute, impregnated jute and activating agents via thermogravimetric analysis were conducted first. Yield and iodine adsorption number were employed to determine the optimal activation conditions. As a result, activation by H3PO4 was best conducted at 700 °C for 90 min with an impregnation ration of 1.0 while conditions for ZnCl2 were 500 °C, 60 min and impregnation ratio of 1.0. That is, the best activation conditions varied with activating agents. So were the properties of resultant jute-based activated carbons. H3PO4 activation produced an activated carbon that was mostly mesoporous while that by ZnCl2 was more even in micropore and mesopore volumes as proven by pore volume distribution analysis. In addition, both carbons were abundant in surface functional groups which could be beneficial for adsorption of pollutants. Overall, jute could be effectively recycled to produce activated carbon that boasted excellent surface chemistry and textual properties.

Activation-pyrolysis of textile wastes was considered a sustainable technique to fabricate activated carbon. Highly mesoporous activated carbon was prepared from waste polyester textiles by employing MgCl2 as the activation and template agents. The influences of different preparation conditions on textual property and crystalline structure of carbon were identified by N2 adsorption-desorption isotherms and X-ray diffraction. The optimum pyrolysis temperature, time and mixing ratio for MgCl2/waste polyester textiles are 900 °C, 1.5 h and 5:5 with the carbon thus obtained manifested a surface area of 1307 m2/g, total pore volume of 3.56 cm3/g of which 98% is mesopore. The effect of MgCl2 on the full-cycle pyrolysis pathway of waste polyester textiles was systematically investigated by various characterization methods to explore the pore-forming mechanism of activated carbon. The results demonstrated that MgCl2 was capable of catalyzing the dehydrogenation, decarboxylic and cross-linking reaction of waste polyester textiles and inhibited the formation of tars during pyrolysis process, indicating that the addition of MgCl2 was conducive to the formation of carbonaceous materials and open pores. Meanwhile, acted as the template, MgO particles derived from the decomposition of MgCl2 could develop massive homogeneous mesopores in the carbon matrix.

Two-step physical activation was used to prepare activated carbon from textile waste jute. Raw material was first carbonized under nitrogen and then activated by CO2. Based on yield and pore structure, the optimal carbonization temperature and time were 500 °C and 60 min, respectively. Carbonized sample was next activated. The development of porosity and surface chemistry was highly dependent on activation temperature and time. Activated carbon produced at 800 °C was predominantly microporous while that produced at 900 °C was more mesoporous and macroporous. The shift from microporosity to mesoporosity could be used to produce either microporous or mesoporous carbon just by changing the activation temperature. Activation also changed the surface chemistry and created a more carbonaceous structure. The jute-based activated carbon was mostly powdered in form, slightly acidic and effective in adsorbing both heavy metals and organics.

Pyrolysis activation of waste polyester textiles (WPT) was regarded as a sustainable technique to synthesize multi-pore activated carbons. MgO-template method of using MgCl 2 as the template precursor was employed, which possessed the advantages of ideal pore-forming effect and efficient preparation process. The response surface methodology coupled with Box-Behnken design (BBD) was conducted to study the interaction between different variables and optimized preparation conditions of waste polyester textiles based activated carbons. Derived from BBD design results, carbonization temperature was the most significant individual factor. And the maximum specific surface area of 1364 m 2 /g, which presented a good agreement with the predicted response values(1315 m 2 /g), was obtained at mixing ratio in MgCl 2 /WPT, carbonization temperature and time of 5:1, 900 °C and 90 min, respectively. Furthermore, the physicochemical properties of the sample prepared under optimal conditions were carried on utilizing nitrogen adsorption/desorption isotherms, EA, XRD, SEM and FTIR. In addition, the pore-forming mechanism was mainly attributed to the tendency of carbon layer coating on MgO to form pore walls after elimination of MgO and the strong dehydration effect of MgCl 2 on WPT.

Cotton textile waste-based magnetic activated carbon was prepared via simultaneous activation-pyrolysis using FeCl3 as a novel activating agent. The response surface methodology based on the Box–Behnken design method was applied to optimize the preparation parameters and predict the specific surface area of the samples. The optimal activated carbon was obtained at a mass ratio of FeCl3/CTW, activation time and activation temperature of 1.62 : 1, 1 h and 700 °C, respectively. The experimental maximum yield and iodine adsorptive value (32.66% and 714.55 mg g−1) of the resultant carbon were close to that of the predicated response values (34.85% and 783.75 mg g−1), respectively. SEM, N2 adsorption–desorption isotherms, XRD, PPMS, FTIR and pHpzc measurements were conducted to analyze the physicochemical characteristics of the optimal sample. The results showed that the carbon matrix had a high specific surface area of 837.39 m2 g−1 with abundant micropores and acidic surface functional groups, and the saturation magnetization (Ms) was 5.2 emu g−1 due to the formation of Fe3O4. The maximum adsorption of Cr(VI) by the carbon reached 212.77 mg g−1. Furthermore, the addition of FeCl3 lowered the pyrolytic carbonization temperature and inhibited the generation of volatiles in the activation-pyrolysis process. Meanwhile, the formation of Fe2O3 and Fe3O4 derived from FeCl3 was beneficial for the development of vast micropores.

In this study, an innovative redox system concerning Fe0-C internal electrolysis combined with sulfite (S(IV)) was first developed for p-nitrophenol (PNP) removal. The effects of different influencing factors including the Fe0/C mass ratio, sulfite concentration, initial pH value and aeration rate were comprehensively investigated in batch experiments. Satisfactorily, the maximum removal and mineralization of PNP reached 92.5% and 59.9%, respectively, in the Fe0-C/S(IV) system. Fe0-C composites with nanosized zero-valent iron anchored on activated carbon had great potential to release Fe2+ and initiate the activation of S(IV). During the reactions, transformation from Fe3+ to Fe2+ was realized, which was attributed to complexation. Significantly, the surface complexation occurred in the diffusion boundary because of the active iron species (Fe(II)–OH) generated on Fe0-C composites, having a remarkable activation effect on S(IV). Furthermore, the reactivity of Fe0-C composites was maintained through the associated effects of the complexation, acid etching and oxidation erosion caused by S(IV). In the end, quenching and ESR experiments illustrated that HO and SO4 − were the dominant free radicals, combined with the subordinate participation of SO3 − and SO5 −. Reduction and oxidation collaborated efficiently to degrade PNP, and Fe0-C internal electrolysis and S(IV) mutually promoted each other in the process, which fully motivated strong the potential of this Fe0-C/S(IV) system to deal with toxic and refractory wastewater.

Activated carbons with high specific surface areas were produced, utilizing waste polyester textiles as carbon precursor by magnesium oxide (MgO) template method. Magnesium chloride (MgCl2), magnesium citrate (MgCi), and MgO were employed as MgO precursors to prepare activated carbons (AC-MgCl2, AC-MgCi, and AC-MgO). Thermogravimetry-differential scanning calorimetry was conducted to investigate the pore-forming mechanism, and N2 adsorption/desorption isotherms, XRD, SEM-EDS, TEM, FTIR and pHpzc were achieved to analyze physicochemical characteristics of the samples. The specific surface areas of AC-MgCl2 (1173 m2/g) and AC-MgCi (1336 m2/g) were much higher than that of AC-MgO (450 m2/g), and the pores sizes of which were micro-mesoporous, mesoporous, and macropores, respectively, due to the formation of MgO crystal with different sizes. All activated carbons had abundant acidic oxygen groups. In addition, batch adsorption experiments were carried out to investigate the adsorptive characteristics of the prepared activated carbons toward Cr(VI). The adsorption kinetics fitted well with the pseudo-second order, and the adsorptive capacity of AC-MgCl2 (42.55 mg/g) was higher than those of AC-MgCi (40.93 mg/g) and AC-MgO (35.87 mg/g).

Ascorbic acid (AsA) has high antioxidant activities, and its biosynthesis has been well studied by engineering of a single structural gene (SG) in staple crops, such as tomato (Solanum lycopersicum). However, engineering the AsA metabolic pathway by multi-SG for biofortification remains unclear. In this study, pyramiding transgenic lines including GDP-Mannose 3&prime, 5&prime, epimerase (GME) &times, GDP-d-mannose pyrophosphorylase (GMP), GDP-l-Gal phosphorylase (GGP) &times, l-Gal-1-P phosphatase (GPP) and GME &times, GMP &times, GGP &times, GPP, were obtained by hybridization of four key genes to get over-expression transgenic plants (GME, GMP, GGP, and GPP) in tomato. Pyramiding lines exhibited a significant increase in total ascorbate in leaves and red fruits except for GGP &times, GPP. Expression analysis indicated that increased accumulation of AsA in pyramiding transgenic lines is due to multigene regulation in AsA biosynthesis. Substrate feeding in leaf and fruit suggested that AsA biosynthesis was mainly contributed by the d-Man/l-Gal pathway in leaves, while alternative pathways may contribute to AsA accumulation in tomato fruit. Pyramiding lines showed an enhanced light response, stress tolerance, and AsA transport capacity. Also, fruit shape, fruit size, and soluble solids were slightly affected by pyramiding. This study provides the first comprehensive analysis of gene pyramiding for ascorbate biosynthesis in tomato. SGs pyramiding promotes AsA biosynthesis, which in turn enhances light response and oxidative stress tolerance. Also, the data revealed an alternative ascorbate biosynthesis pathway between leaves and fruit of tomato.

Power loss impacting the thermal performances, operating precision and even service life of angular contact ball bearings has not been thoroughly addressed so far. Evidently, ignoring the effect of vibration on heat generation may be partly responsible for the difference. This paper devotes to the thermal estimation on angular contact ball bearings with vibration effect. The experiments about vibration effect on bearing temperature were first implemented. To explore the causes, the energy exchange in vibration was discussed and then the shaft-bearing system was simplified to a forced vibration model to analyze the bearing loads in vibration. Considering the contact stiffness and damping between balls and rings, the instantaneous force balance equations were built. Next, the vibratory-induced additional load and additional spin power loss of balls was proposed successively. The vibration-induced heat was integrated into a novel forecasting model of bearing power loss. For validation, the muti-node model for angular contact ball bearings was referred to create the thermal network of spindle front bearing, and then the contrast and discussion were done. The excitation force and vibration response, meanwhile, were also measured to validate the developed model further. With the help of improved heat generation model, the bearing temperature rise can be better forecasted.

Hypersonic vehicles are enveloped by a plasma sheath that affects the data transmission and object identification. This paper develops a numerical methodology based on Magnetohydrodynamics equations to study the electromagnetic environment of hypersonic vehicles under the condition of carbon-based thermal protection material ablation. A surface ablation model considering the oxidation and sublimation ablation process is coupled with a Navier–Stokes solver by a gas–solid interaction method to simulate the ablation plasma flows. A piecewise linear current density recursive convolution finite-difference time-domain method is applied to further analyze the interaction between the incident electromagnetic wave and the plasma sheath. The computational results for an HTV-2 type vehicle indicate that both ablation and non-ablation plasma sheaths have significant effects on the electromagnetic environment of the vehicle. Compared with a non-ablation plasma sheath, ablation results in a decrease in the number of electrons and increases the number of neutral particles and therefore changes characteristic parameters of the plasma. Details of the electromagnetic scattering characteristics are reported to highlight the influences of ablation on the reflectivity, penetrability, and absorptivity of the plasma sheath for incident electromagnetic waves over different bands.

In this study, the reduction of iron-carbon internal electrolysis was reinforced by persulfate for p-nitrophenol removal. The effects of persulfate dosage, initial pH and iron-carbon mass ratio were comprehensively studied in batch experiments. In the system of iron-carbon internal electrolysis coupled with persulfate, the iron-carbon internal electrolysis and persulfate had a significant mutual influence, exhibiting a wide range of pH in the treatment process. Moreover, the coupled system also showed the remarkable removal and degradation efficiency of p-nitrophenol according to the contrast experiments. The satisfactory results should be attributed to the potential reduction of iron-carbon internal electrolysis, which was stimulated by persulfate to transform the nitro group to the amine group, accompanying the subsequent oxidation. Furthermore, persulfate possessed the ability that the dynamically destructive effect on external and internal of Fe0 and the scavenging action on activated carbon, effectively strengthening the potential energy for release and transfer of reductive substances. Both HO• and SO4•- as the main free radicals were formed to mineralize the intermediates in the coupled system. These findings indicate that the system of iron-carbon internal electrolysis coupled with persulfate can be a promising strategy for the treatment of the toxic and refractory wastewater.

FeCl3 is a valuable iron salt used in the synthesis of magnetic waste cotton woven-based activated carbon. Although it has received extensive research attention, more information is required regarding its interactions with the carbon matrix. This systematic study describes the potential reactions of FeCl3 and waste cotton woven. First, the textural properties of waste cotton woven-based activated carbon synthesized under various conditions were investigated via element analysis, N2 sorption/desorption isotherms, and scanning electron microscopy. Then, the possible reaction mechanisms were deduced through various characterization methods. The results demonstrate that FeCl3 can lower the initial decomposition temperature of WCW to 135 °C and catalyze decarboxylation and decarbonylation at 100–330 °C to elevate the formation of microporous structures. Moreover, FeCl3 can also form Lewis acid sites at 330–700 °C and promote the cross-linking reaction to develop intricate microporous structures and carbonaceous materials with the synergistic effect of Fe3+ and Cl−. FeCl3 could be used as a template-like agent to form mesoporous structures. Meanwhile, it can also act as a magnetizer that Fe3O4 derived from the decomposition of FeCl3 would insert into the carbon matrix and combine with C–Cl to tailor the magnetic controllable activated carbon. Finally, we confirmed that extending the activation time could convert the structure of waste cotton woven-based activated carbon and increase the number of active sites, thereby further improving the catalytic properties of FeCl3 in pore formation.

Spectral peak (SPEAK) algorithm is one of the most popular speech processing strategies in cochlear implant (CI). SPEAK-based speech processing strategy adopts filter bank to split frequency band, and provides some stimulating channels to CI electrode array. In this paper, we analyze the parameter feature for SPEAK-based speech processing strategy, adding to its theoretical and engineering value in algorithm research of new speech processing algorithm.

Present speech recognition of cochlear implant is still low for situation of noisy environment or under mismatch condition, and more researches focus on improving front-end signal acquisition and speech recognition. To simplify signal acquisition and algorithm research, we develop an intelligent terminal-based signal acquisition system for cochlear implant, in which the electric relay and many sensors are adopted to implement system monitoring function. The proposed system platform is helpful to actualize algorithm research and intelligent monitoring, adding to its value of further research of speech recognition improvement.

Activated carbon-supported nano zero valent iron was synthesized through a carbonthermal reduction process. Specifically, iron-impregnated activated carbon was thermally treated under N2 atmosphere at temperatures ranging from 350 to 1,150°C. Major properties of the synthesized materials were obtained through analysis of iron content, BET surface area, and pore size distribution. TEM images, X-ray diffraction (XRD), and Fourier transform infrared patterns were also obtained for characterization. Results show that zero valent iron was reduced from iron oxide and those nanoparticles were highly dispersed based on TEM images while XRD patterns indicate a progressive reduction of iron oxide to form elemental iron. Treatment temperature greatly impacted the characteristics of the carbonthermal products. The size of the particles, content of elemental iron, surface functional groups, and pore structure all changed with the change in treatment temperature. Synthesized materials were tested for their reac...

Cochlear implant was traditionally equipped with one omni-microphone, and directional microphone has been applied in present papers and products. Microphone array based methods use space information to differentiate the desired signal and ambient noise. Delay value is an important parameter in beamforming, which determine the beam pattern. In the application of cochlear implant front-end signal acquisition, we need to solve the fractional delay problem as small distance between microphones. The proposed least mean square error rule can minimize the average error for the whole frequency band. And the fractional delay filter characteristic and mismatch are analyzed to help to further algorithm application in front-end beamforming for cochlear implant.

A new hybrid material was prepared by loading the nanoscale iron oxide particles within the pores of granular activated carbon (GAC-NSIO) and used as adsorbent to remove Cd(II) in aqueous phase. The new material is characterized by the pHpzc, TEM, XRD, BET, and XPS analytical techniques to deduce the potential adsorptive mechanism, and further it along with GAC were assessed in the removal of Cd(II) from aqueous solution for various physico-chemical factors iron-loaded content, pH, humic acid, isotherm, kinetics, and thermodynamics, under the batch reactor studies and rapid small-scale column tests also appended dealing with the breakthrough volume. Characterization of adsorbent indicated that the amorphous nanoscale iron oxides were successfully immobilized on GAC. Adsorption mechanism mainly included surface complexation, Donnan membrane effect, and electrostatic attraction. The optimum iron-loaded content of GAC-NSIO was 17%. The adsorption process was more favorable at high pH, and iron oxide ...

Activated carbon derived from waste cotton textiles (WCT) was synthesized using FeCl3 as an activating agent. The influence of pyrolysis temperature on the physiochemical properties of activated carbon were examined by XRD and XPS analysis. The carbonaceous materials participated in the transformation of Fe species by carbothermal reduction. Abundant acidic surface functional groups appeared during pyrolysis of WCT in the presence of FeCl3. According to the TG-FTIR-GC–MS technique, FeCl3 significantly influenced the pyrolysis behavior of WCT. The major carbonization temperature was reduced from 350 to 163 °C due to the catalytic cleavage of glycosidic bonds and cellulose chains over FeCl3. In addition, the release of CO2 and H2O(g) via decarboxylation, carbonyl group cracking and cross-linking reactions contributed to the pore development. Furthermore, the maximum adsorption capacity of Cr(VI) for the prepared adsorbent was 267.12 mg/g and the adsorption was fitted with the pseudo-second-order model and the Langmuir isotherm model. The adsorption mechanism was mainly driven by electrostatic attraction, reduction, and complexation.

Five cationic surfactants were employed to modify activated carbon for the purpose of comparing the impacts of surfactant properties and operational parameters on modification. Surfactants under study included cetylpyridinium chloride monohydrate (CPC), hexadecyltrimethylammonium bromide (HDTMA), cetyltrimethylammonium chloride (CTAC), myristyltrimethylammonium bromide (MTAB), and decyltrimethylammonium bromide (DTAB). Results revealed that, properties of surfactants (critical micelle concentration, chemical configuration), initial loading concentration, pH of solution and carbon type all had significant impacts on surfactant loading. In general, surfactants with smaller micelle structures were more easily loaded than those with larger micelles. For all cationic surfactants tested here, loading is optimal around neutral pH. After surfactant loading, activated carbon presented a much positively charged surface and this is manifested in obvious improvement in perchlorate adsorption. Perchlorate was mainly adsorbed through ion exchange with surfactant-loaded activated carbon.

Nanozero-valent iron/activated carbon (nZVI/AC) composite is investigated as a possible stabilization agent for heavy metals in river sediment. Effects of stabilization were tested by leaching tests such as synthetic precipitation leaching procedure (SPLP), atoxicity characteristic leaching procedure (TCLP), and a horizontal method that simulates various environmental conditions. In addition, changes in heavy metal forms before and after the addition of nZVI/AC were studied via sequential extraction method. Heavy metals such as Cu, Cd, and Pb were effectively stabilized by nZVI/AC. The stabilization could be attributed to the changes in bonding of heavy metal with sediment. The nZVI/AC in sediment increased the fraction of strongly bound heavy metals. Investigations on the impacts of nZVI/AC dosage, particle size, and time on stabilization and metal speciation showed that they all had significant effects. Generally, leaching dropped as dosage increased and a high dosage led to more metals in stron...

Cationic surfactants were employed to modify granular activated carbon (GAC) for the purpose of improving GAC’s adsorption of arsenate from water. Rapid small-scale column tests (RSSCTs) were set up to test the adsorption capacities. Results indicated that surfactant cetyltrimethylammonium chloride (CTAC) modification manifested the highest improvement in GAC’s adsorption for arsenate. GAC modified by 2 mmol/L of CTAC was able to operate approximately 64,000 bed volumes before 10 μg/L of arsenate breakthrough as compared with 2,100 bed volumes for virgin GAC. GAC also performed much better than zeolite and bentonite both in surfactant retention and arsenic removal. Arsenate adsorption was affected by influent concentration, pH, and presence of other anions. The effect of competitive anions on arsenate adsorption was in the order of PO43->SO42->NO3-. Breakthrough tests on tap water spiked with arsenate indicated that the modified GAC had high selectivity for arsenate and considerable amount of ar...

We utilized 234Th, a naturally occurring radionuclide, to quantify the particulate organic carbon (POC) export rates in the northern South China Sea (SCS) based on data collected in July 2000 (summer), May 2001 (spring) and November 2002 (autumn). Th-234 deficit was enhanced with depth in the euphotic zone, reaching a subsurface maximum at the Chl-a maximum in most cases, as commonly observed in many oceanic regimes. Th-234 was in general in equilibrium with 238U at a depth of ∼100 m, the bottom of the euphotic zone. In this study the 234Th deficit appeared to be less significant in November than in July and May. A surface excess of 234Th relative to 238U was found in the summer over the shelf of the northern SCS, most likely due to the accumulation of suspended particles entrapped by a salinity front. Comparison of the 234Th fluxes from the upper 10 m water column between 2-D and traditional 1-D models revealed agreement within the errors of estimation, suggesting the applicability of the 1-D model to this particular shelf region. 1-D model-based 234Th fluxes were converted to POC export rates using the ratios of bottle POC to 234Th. The values ranged from 5.3 to 26.6 mmol C m−2d−1 and were slightly higher than those in the southern SCS and other oligotrophic areas. POC export overall showed larger values in spring and summer than in autumn, the seasonality of which was, however, not significant. The highest POC export rate (26.6 mmol C m−2d−1) appeared at the shelf break in spring (May), when Chl-a increased and the community structure changed from pico-phytoplankton (

Iron-impregnated activated carbons have been found to be very effective in arsenic removal. Oxyanionic arsenic species such as arsenate and arsenite adsorb at the iron oxyhydroxide surface by forming complexes with the surface sites. Our goal has been to load as much iron within the carbon pores as possible while also rendering as much of the iron to be available for sorbing arsenic. Surface oxidation of carbon by HNO 3 /H 2 SO 4 or by HNO 3 /KMnO 4 increased the amount of iron that could be loaded to 7.6–8.0%; arsenic stayed below 10 ppb until 12,000 bed volumes during rapid small-scale tests (RSSCTs) using Rutland, MA groundwater (40–60 ppb arsenic, and pH of 7.6–8.0). Boehm titrations showed that surface oxidation greatly increased the concentration of carboxylic and phenolic surface groups. Iron impregnation by precipitation or iron salt evaporation was also evaluated. Iron content was increased to 9–17% with internal iron-loading, and to 33.6% with both internal and external iron loading. These iron-tailored carbons reached 25,000–34,000 bed volumes to 10 ppb arsenic breakthrough during RSSCTs. With the 33.6% iron loading, some iron peeled off.

Nano-zero-valent iron/activated carbon (nZVI/AC) composite was evaluated for its effectiveness in the stabilization of Cu, Pb, Cd, and Cr in dredged river sediment. Synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP) were adopted to compare the effects of nZVI/AC dosage, particle size, time duration, and temperature on heavy metal leachability. The results show that leachability dropped considerably with the addition of nZVI/AC and powdered particles in the size of 0.075-0.18 mm was more effective in stabilization than granular ones. Stabilization effect was stable in long-term and robust against changes in temperature. Tessier sequential extraction revealed that heavy metals were associated with solid particle, inorganic or organic matters in sediment. The addition of nZVI/AC was able to convert relatively weakly bound heavy metals into more strongly bound species and thus reduce the bioavailability and toxicity. Also, the standard potential of heavy metals may decide the mechanism of stabilization process.

Thermal reactivation with CO2 or NH3 at temperatures higher than 700 °C effectively restored the perchlorate adsorption capacity of ammonia-tailored carbon. In contrast, steam regeneration restored only a portion of the perchlorate adsorption capacity, and these distinctions were attributed to the change in surface chemistry that was induced by regeneration. After perchlorate loading, regenerating the ammonia-tailored GAC via CO2 or NH3 preserved the nitrogen content and positive surface charge density of the initial ammonia-tailored activated carbon. In contrast, steam regeneration caused a decrease in nitrogen content and positive surface charge. Perchlorate breakthrough was monitored in rapid small-scale column test (RSSCT) operations with either CO2 or NH3 regeneration. 4000–4500 bed volumes of perchlorate adsorption life could be achieved through at least three cycles of RSSCT operation and regeneration. This compared favorably to the 4500 bed volumes that had been achieved when using the initial ammonia-tailored carbon.

Thermal tailoring of a bituminous granular activated carbon (GAC) by ammonia gas at 500–800 °C for 60 min achieved as much as 4-fold improvement in perchlorate adsorption as determined by rapid small-scale column tests (RSSCTs). When treating natural groundwater that contained 70–78 ppb perchlorate, the bed volumes to 4 ppb perchlorate breakthrough increased from 1100 bed volumes for commercial bituminous carbon up to 4400 bed volumes for carbon that was tailored in ammonia at 700 °C. Increased perchlorate adsorption corresponded to increased positive surface charges with R2 0.956. The increase in positive surface charge was closely related to the increase in nitrogen content after ammonia tailoring. The ammonia-tailored activated carbons also exhibited a moderate increase in TOC removal and higher selectivity for erchlorate. The work herein interfaces with a companion paper by the same authors in which the ammonia-tailored carbon surfaces are characterized relative to physical–chemical features [1] .

A commercially available bituminous granular activated carbon (GAC) was subjected to thermal treatment with ammonia for 60 min at temperatures of 500–800 °C. The effect of this treatment on the physical and chemical characteristics of carbon was studied in detail. Comparison of virgin and NH3-tailored carbons relative to pore volume distribution and argon-BET surface area indicated that ammonia acted as an activating agent under these conditions. Micropore volume increased with increasing treatment temperature up to 700 °C; and then declined at 800 °C. Elemental analysis results showed that nitrogen was incorporated into the carbon matrix during the thermal treatment as proven by an increase in N-content from 0.64% for virgin GAC up to 1.61–1.63% for all the tailored samples. The ammonia treatment caused an increase in positive surface charge density over a broad pH range; and this was reflected in a higher pHpzc and pHIEP. This was attributed to the more basic nature of the carbon surface after its treatment in ammonia.

Cationic surfactant cetyltrimethylammonium chloride (CTAC) was employed to tailor-activated carbon, granular ferric hydroxide (GFH), chitosan, zeolite, and bentonite so as to investigate the effect of CTAC tailoring on perchlorate adsorption. Surfactant loading varied with adsorbent. Surface porosity and ion exchange capacity all contributed to surfactant loading. In particular, bentonite and activated carbon showed the highest loading of surfactant. In comparison, chitosan was able to contain only a negligible amount of CTAC. One direct effect of CTAC tailoring was the increase of adsorbent’s surface point of zero charge pHpzc. However, the extent of pHpzc change differed with adsorbents, and this is attributed to the differences in interactions between surfaces and CTAC. The CTAC loading on activated carbon is more likely attributable to hydrophobic-hydrophobic interaction, whereas CTAC’s was anchored onzeolite and bentonite by interaction between the hydrophilic head of CTAC and surface. Also, ...

The authors have combined corrosion of steel fittings or perforated sheets with granular activated carbon (GAC) that had been pre-treated with Fe(III)-citrate, to produce an innovative and low-maintenance technique for removing arsenic from groundwater. Removal of arsenic was measured using two GAC column configurations: rapid small scale column tests (RSSCT's) and mini-column tests. Independent variables included pH, pre-corrosion procedure, and idling of the column (i.e. intentionally stopping flow for defined times in order to create reducing conditions). Use of corroded steel plus pre-treated GAC removed arsenic to below 10 μg/L for up to 248,000 bed volumes (BV) at pH 6, compared to 7,000 BVs for pre-treated GAC without pre-corroded steel. Performance was not as good at pH 6.5 or 7.5. Idling the system recovered the iron corrosion ability by reducing the passive Fe(III) layer on pre-corroded steel surface, as a result the BVs to arsenic breakthrough was doubled. But idling also caused brief periods of arsenic and iron release after restart, due to reductive dissolution of arsenic-containing ferric oxides. GAC was also effective as filtration media for removal of iron (hydr)oxide particles (and associated arsenic) that was released from the pre-corroded iron.

Arsenic is of concern in water treatment because of its health effects. This research focused on incorporating hydrous ferric oxide (HFO) into granular activated carbon (GAC) for the purpose of arsenic removal. Iron was incorporated into GAC via incipient wetness impregnation and cured at temperatures ranging from 60 to 90 degrees C. X-ray diffractions and arsenic sorption as a function of pH were conducted to investigate the effect of temperature on final iron oxide (hydroxide) and their arsenic removal capabilities. Results revealed that when curing at 60 degrees C, the procedure successfully created HFO in the pores of GAC, whereas at temperatures of 80 and 90 degrees C, the impregnated iron oxide manifested a more crystalline form. In the column tests using synthetic water, the HFO-loaded GAC prepared at 60 degrees C also showed higher sorption capacities than media cured at higher temperatures. These results indicated that the adsorption capacity for arsenic was closely related to the form of iron (hydr)oxide for a given iron content For the column test using a natural groundwater, HFO-loaded GAC (Fe, 11.7%) showed an arsenic sorption capacity of 26 mg As/g when the influent contained 300 microg/L As. Thus, the preloading of HFO into a stable GAC media offered the opportunity to employ fixed carbon bed reactors in water treatment plants or point-of-use filters for arsenic removal.

During a spring intermonsoon cruise in 2004, depth profiles of total and particulate Th-234 in the upper 100 m were collected at 36 stations in the southern South China Sea (SCS), covering a surface area of similar to 1.0 x 10(6) km(2). Thorium-234 was sampled by using a modified small-volume MnO2 co-precipitation technique, which allows mapping the Th-234 distribution with a high spatial resolution. A stratified structure of Th-234/U-238 disequilibria was generally observed in the upper 100 m water column, suggesting that the euphotic zone of the southern SCS in this season can be separated into two layers: an upper layer with low export production rates and a lower layer with high export production rates. At the same time, we observed extensive zones of Th-234 excess within the euphotic layer, which is possibly due to intense remineralization of particulate matter. Particulate organic carbon (POC) export was estimated from a three-dimensional steady state model of Th-234 fluxes combined with measurements of the POC/Th-234 ratio on suspended particles. The POC export for this region varied from a low of -10.7 +/- 1.5 mmolC m(-2) d(-1) to a high of 12.6 +/- 1.1 mmolC m(-2) d(-1), with an average of 3.8 +/- 4.0 mmolC m(-2) d(-1). A negative flux of POC export is interpreted as the result of lateral input of particulate matter from nearby waters. Regional patterns in POC export show enhanced fluxes along the western and southern boundaries of the study region, and a "tongue'' of low export extending northwestward from similar to 7 degrees N 116 degrees E to similar to 10 degrees N 111 degrees E. This geographic distribution is consistent with the overall surface circulation pattern of the southern SCS in this season.