Different Amounts Of Sulfur Research Articles

Kükürtlenmiş Kayısıların Raf Ömrünü Uzatmada Kükürtün Etkisinin Kinetik İncelenmesi

In this study, sulphurized apricots with different sulfur values were obtained from the factory in Malatya province. These apricot samples were kept at market temperature values (4, 26 and 40°C) in the package offered for sale, and their sulfur dioxide values were determined daily. As a result of the experimental periods, reduction rate and other data were determined by calculating the sulfur dioxide in the sample. Also, loss rate and kinetics of sulfur dioxide were determined from its change over time at different temperatures. From the results obtained, important findings such as shelf life of sulphurous apricots at different temperatures in the package, deterioration and effect of the sulfur dioxide value on the shelf life were obtained. According to the analysis results of apricots containing different amounts of sulfur, when the moisture and SO2 loss in dried apricot samples during their stay on the shelf were examined in the kinetic study, it was determined that it was suitable for the first order kinetic model for 4°C and the second order kinetic model for 26 and 40°C. From the experimental results, quite low sulfur removal values were obtained for the samples offered for sale after 980 hours at 4°C and 525 hours at 26°C. Moisture and SO2 losses accelerated after approximately 740 hours at a temperature of 40°C. In the sample containing 3280 ppm sulfur dioxide during shelf storage at 4°C, there was an 11% loss of sulfur dioxide after 980 hours. A 46% sulfur dioxide loss was determined in the same samples after 740 hours at 40°C. It has been determined that sulfur dioxide loss is greater at higher temperatures. When the storage conditions of the samples were examined in terms of humidity, it was observed that apricots lost their moisture in the range of 52-85% after 29 days at temperatures of 4 and 40 °C. Based on the fact that the water activity of the packaged sulfurized dried apricots offered for sale is 25%, in this study, an average shelf life of approximately 25 days was determined according to this value.

A physicochemical model-based digital twin of Li–S batteries to elucidate the effects of cathode microstructure and evaluate different microstructures

We are presenting a physicochemical model-based digital twin of Li–S batteries which involves continuum, volume-averaged ion transport equations including species migration, dissolution and precipitation, and electrochemical reactions, where the cathode microstructure is taken into account in terms of pore size distribution, hierarchy and tortuosity. The digital twin is applied in simulations of galvanostatic charge-discharge of a Li–S cell, exploring three types of cathode microstructure, activated carbon, graphene and hollow particles, two different amounts of sulphur and two different cathode coating thicknesses. Very good agreement is observed between predictions and experimental data in all case-studies. The best cathode is 70 wt% sulphur in host with porous hollow particles which trap the polysulphides from migrating to the anode. The simulations reveal that other reasons for low sulphur utilization, preventing the Li–S cell from reaching its theoretical capacity, are undissolved sulphur in micropores and sulphur leaching to macropores, especially in the cathode region near the separator, and reprecipitating.

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Correlation between some physical properties of pure and Sb doped Cu2SnS3 thin films under the effect of sulfur amount for solar cell application

Adjusting of sulfur content and amount of doping in Cu2SnS3 (CTS), as absorber layer for solar cell, is a promising approach to fabricate thin film solar cells with high performance. In this work, the effect of different amounts of sulfur in the sulfurization process and the percentage of Sb doping in the films were studied. The physical properties of un-doped and doped CTS thin films were investigated. The pure and doped CTS thin films showed a monoclinic structure, with a larger grain size under the influence of Sb doping. XPS analysis demonstrated that Cu, Sn, S, and Sb oxidation states were +1, +4, −2, and +3, respectively. The Sb-doped sample for 25 min (25Sb) has a higher Cu+1/Cu+2 ratio than other samples and no satellite peak of Sn+2 was observed as compared to other levels of doping samples. This concluded that the Cu species in the 25Sb film experienced a more Cu-rich chemical environment. Both PL and UV–Vis spectroscopy were used to obtain the optical properties. Hall Effect was applied to measure the electrical properties of un-doped and doped CTS films. The pure and Sb-doped CTS solar cells were fabricated by optimization of Sb doping time and sulfur amount. The conversion efficiency of the prepared solar cell was 2.13% when fabricated with CTS layer that treated with 25 min of Sb doping and 100 mg of sulfur, whereas the efficiency of the un-doped CTS solar cell at the same sulfur amount was just 0.615%.

Effect of High Content of Waste Tire Rubber and Sulfur on the Aging Behavior of Bitumen

High content rubber modified bitumen (HCRMB) prepared from the high content of waste tire rubber and bitumen has good performance while allowing greater use of the waste tires. However, HCRMB is subject to aging during use, which can affect its performance. The purpose of this paper was to investigate the effect of high content of waste tire rubber and sulfur on the aging behavior of bitumen. The properties of all bitumen were tested using rolling thin film oven aging (RTFOT) test, pressure aging vessel (PAV) test, frequency sweep tests, temperature sweep (TS) test, multiple stress creep recovery (MSCR) test, and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) test. Test results show that the addition of sulfur to HCRMB leads to an improvement in the elasticity of HCRMB. The elasticity of HCRMB with different amounts of sulfur increases with aging. In addition, the increase in the amount of sulfur can improve the RTFOT aging resistance and the PAV aging resistance of HCRMB. Sulfur cannot reduce the degree of oxidation of HCRMB after aging, but can inhibit the degree of desulfurization of HCRMB. Furthermore, the aging process of HCRMB with different amounts of sulfur is dominated by the degradation of polybutadiene.

Tin Sulfide Chalcogel Derived SnSx for CO2 Electroreduction

A new class of aerogels based exclusively on metal chalcogenide frameworks has been developed, opening up a series of novel properties and applications. Further expanding the application of such chalcogels in electrocatalytic CO2 reduction is of significance for mitigating the rise of atmospheric CO2 concentration. Herein, the tin sulfide chalcogel was employed as a pre-catalyst for the construction of efficient electrocatalysts for CO2 reduction. SnS0.09 and SnS0.55 supported on carbon cloth (SnS0.09/CC and SnS0.55/CC) were obtained with different amounts of sulfur by cyclic voltammetry activation of the tin sulfide chalcogel at different potential intervals. Compared to SnS0.09/CC, SnS0.55/CC with higher S content exhibited higher formate Faraday efficiency of 93.1% at -1.1 V vs. RHE, and the partial current density of formate was 28.4 mA/cm2. The difference in performance between SnS0.09/CC and SnS0.55/CC could be attributed to the varying sulfur which could favor the formation of formate.

Does the high sulfur content in apricots affect oxidative stress?

Apricots are one of the most important fruits that can be produced worldwide. Most of the importer countries are sensitive about sulfur which is used in the protection of dried apricots. The objective of this study was to compare the effects of feeding with high and low sulfur content apricots on oxidative stress parameters of the liver. In total, 42 Wistar albino rats were fed for 12 weeks with the use of dried apricots containing different amounts of sulfur and sun-dried apricots. There was no significant difference in IL-1β, 8-OHdG and TOS levels between the control group and the group fed with sun dried apricots. There was no statistically significant difference between the groups fed with low and high sulfur-containing apricots.Non-necrotic changes were observed in 3000 ppm and 4000ppm groups in microscopic examination. No significant effect of feeding with sulfur treated apricots was found in the liver tissues of rats.

Selection of Soybean Genotypes under Different Amounts of Sulfur Using Multivariate Statistical Methods

Selection of Soybean Genotypes under Different Amounts of Sulfur Using Multivariate Statistical Methods

NiSe2@NixSy nanorod on nickel foam as efficient bifunctional electrocatalyst for overall water splitting

Electrocatalytic water splitting technology has become one of the most promising methods to solve the energy crisis, which can produce a large amount of high purity H2 and O2. It is necessary to develop efficient and stable water splitting catalyst for reducing the overpotential of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and accelerating their reaction kinetics. A series of NiSe2@NixSy nanoarrays was firstly in situ grown on the nickel foam through the typical hydrothermal, selenylation and sulfuration pathways. The Na2SeO3 homogeneous solution is formed by hydrothermal and the selenization process is done at the temperature of 180。C. Then the nickel foam (NF) is put into the Na2SeO3 solution to form NiSe2 material at the temperature of 120。C. After that, the NiSe2 materials were sulfuretted with different amounts of sulfur to form NiSe2@NixSy hybrid materials. The experimental results demonstrate that the NiSe2@NixSy material as a 3D electrode can maximize the synergistic reaction between NiSe2 and NixSy, thus exhibiting an efficient and comprehensive water splitting performance. The NiSe2@NixSy-1 material presents a superior OER performance with requiring the overpotential of only 206 mV at 100 mA cm−2. Moreover, the NiSe2@NixSy-0.3 material presents a superior HER performance with requiring the overpotential of only 148 mV at 100 mA cm−2. It is worth noting that when NiSe2@NixSy-1 material and the NiSe2@NixSy-0.3 material was used as cathode and anode, only 1.53 V cell voltage is needed to produce a current density of 10 mA cm−2 throughout the water splitting process, which is one of the smallest values reported so far. Density functional theory calculations results show that the Ni3S2 has the best water adsorption energy, so it is an active species in the process of catalysis. However, NiSe2 has more density distribution around the Fermi level, indicating that it exhibits better metallic properties, which makes the NiSe2@NixSy-1 hybrid material exhibit better electronic conductivity.

The Effect of Network Structure on Compressive Fatigue Behavior of Unfilled Styrene‐Butadiene Rubber

The effect of network structure on dynamic compressive fatigue behavior and static compressive mechanical properties of styrene‐butadiene rubber (SBR) were investigated. A series of SBR compounds with different amounts of sulfur and dicumyl peroxide (DCP) were prepared, and their crosslinking densities were calculated using the Flory–Rehner equation. Compressive fatigue resistance and creep behavior of the vulcanizates were performed on a mechanical testing and simulation (MTS) machine. The fatigue damage surface of SBR vulcanizates before and after a dynamic compressive fatigue test was observed with a scanning electron microscopy (SEM). The results suggested that the surface of the samples was badly damaged as the number of compressive cycles increased. By comparison, compressive fatigue caused less surface damage to sulfur‐cured SBR than to peroxide‐cured SBR. The peroxide‐cured SBR samples showed higher energy dissipation than sulfur‐cured SBR during cyclic compression. The peroxide‐cured SBR showed lower creep strain and compression set than the sulfur‐cured SBR. The ‐Sx‐ linkages provided by the sulfur curing system allow dynamic compressive deformation but suffer from poor static compressive resistance. However, the carbon‐carbon linkages from DCP are irreversible and provide higher resistance to static compressive stress, but they do not show obvious dynamic compressive fatigue resistance.

Increasing Energy Density and Power Density in Hybridised Supercapacitor-Battery Devices

Research is presented aiming to increase both power and energy density of lithium batteries by applying composite cathodes containing sulphur, which has a high theoretical specific capacity of 1675 Ah/kgS and is an abundant and low-cost material, and increase the power density of the cells by creating battery-supercapacitor hybrids with the hybridisation carried out at electrode material level. The focus of current research worldwide has been to increase the cyclability of lithium-sulphur (Li-S) batteries, which has been accomplished by devising composite sulphur cathodes, to avoid cathode degradation due to the expansion of sulphur to accommodate the formation of sulphides, and various functionalisation approaches to trap the sulphides and avoid the ‘shuttle’ effect during charge. However, the theoretical capacity of sulphur has not been achieved even at first discharge, lowering the expected energy density, and this is further compounded by the fact that only a fraction of the composite cathode is sulphur. Modelling studies have shown that access of all sulphur by the Li+ ions in the micropores is critical and formation of sufficient amounts of higher order sulphides during the first stage of discharge is needed, to be able to obtain a long second stage discharge plateau. The first stage of our study is focused on demonstrating homogeneous and deep sulphur impregnation of porous carbonaceous material to create cathodes with more than 50 wt% sulphur in a supercapacitor-type, porous, host matrix. Repeated discharges are carried out after which we have achieved the theoretical specific capacity of sulphur at first discharge (cumulative curve in Figure 1). We shall continue with parametric studies to investigate the effect of different amounts of sulphur in the composite cathode on the pore size distribution and discharge capacity. The second part of this study includes the investigations into lithium battery-supercapacitor cells hybridised at electrode material level, in combinations of parallel and in series material parts in equivalent circuit models. The effect of the supercapacitor porous carbonaceous electrode materials on the voltage of the cell in galvanostatic charge-discharge curves will be presented in experimental investigations for half-cells of both sides and full cells. Some novel cell architectures will be presented aiming at minimising any detrimental reactions in the supercapacitor materials within the battery cell window. Figure 1

Characteristics of Cu2ZnSnS4 thin films formed by precursor solutions with different amounts of sulfur

ABSTRACTCu2ZnSnS4 (CZTS) thin films were fabricated using a precursor solution with controlled amounts of thiourea (CH4N2S) by adjusting the molar ratios of sulfur to Cu, Zn and Sn to 1, 1.25, 1.5, 1.75, and 2 times. The CZTS precursor solution was sprayed on a glass substrate and annealed at 500°C for 1 min. in air to produce the CZTS thin films. From the results of EDX and XRD measurements, it was found that all the CZTS thin films lacked sulfur and crystallized well in the typical CZTS crystal growth plane directions, irrespective of the amount of sulfur contained in the CZTS precursor solution. The optical energy band gap calculated from the transmittance of CZTS thin films was found to be 1.08 – 1.19 eV, which makes it capable for absorption in the entire visible light region. The CZTS thin films formed with a precursor solution having a high molar ratio of sulfur 1.75 and 2.0 showed a very high absorption coefficient of about 5 × 104 cm−1. It is understood that excessive sulfur contained in the CZTS precursor solution increased the light absorption characteristic of the CZTS thin films.

Hydrogen sulfide formation characteristics of pulverized coal combustion – Evaluation of blended combustion of two bituminous coals

Abstract This paper presents the characteristics of sulfur release during pyrolysis and hydrogen sulfide (H2S) formation for the pulverized coal combustion of blends of two bituminous coals in a pulverized coal combustion test furnace. The amount of sulfur released during pyrolysis is affected by the total sulfur content and the form of sulfur. Organic sulfur is more readily released to the gaseous phase than pyritic sulfur and sulfate sulfur. When blends of two bituminous coals releasing different amounts of sulfur are fired, the H2S concentrations are between those for the combustion of the single coals. The peak H2S concentration in the near-burner region in the blended combustion coincides with the value estimated from the blending ratio, which means that there is no interaction between the sulfur releases of the two coals during pyrolysis. The reaction behavior of H2S and SO2 after the release of sulfur during the blended combustion is the same as that in the combustion of each single coal.

Thermorheology of Polyethylene Wax Modified Sulfur Asphalt

Abstract The possibility of using polyethylene (PE) wax to modify the rheology of sulfur asphalt binders is investigated. In this study, two industrial wastes namely sulfur and PE wax are used to modify asphalt for pavement applications. Asphalt binders with different amounts of sulfur and wax content are prepared in a high shear blender and rheological tests were carried out in ARES rheometer. PE wax content was varied from 2 to 8 % and sulfur of up to 40 % is used in asphalt binder. Melt rheology is characterized by dynamic frequency sweep, temperature sweep and artificial ageing techniques. Pure and modified asphalt binders are also characterized by Fourier transform infrared spectra (FTIR). Improvement in the viscoelastic properties (G′ and G″) of the sulfur asphalt binders is obtained due to the addition of PE wax. PE wax modification has reduced temperature susceptibility of sulfur asphalt and increased the upper performance temperature. In addition, this wax modification has increased the activation energy and the zero shear viscosity of sulfur asphalt. Optimum sulfur and PE wax contents of the asphalt binder are recommended. Utilization of PE wax and sulfur wastes in asphalt modification proved to enhance asphalt pavement life.

Effects of sulphur addition on modification and mechanical properties of sand cast A1-2wt% Alloy

The effects of sulphur addition on the microstructure and mechanical properties of sand cast Al-12wt%Si alloy have been investigated in this study. For this purpose, different amounts of sulphur were added to Al-12wt%Si alloy in an induction furnace to produce sand castings for micro-structural and mechanical properties analyses. Tensile and hardness tests were carried out to determine the mechanical properties while optical microscopy was used to investigate the microstructure of the cast samples. The results showed that the addition of sulphur to Al-12wt%Si alloy modified the Al-Si eutectic morphology from needle-like (flake-like) eutectic silicon structure to fine-globule eutectic silicon structure. The optimum modification level of sulphur was found to be 0.02-0.05% of the weight of the alloy. Increase in concentration of sulphur above the optimum level of modification decreased the degree of fineness of the eutectic silicon structure with significant decrease in mechanical properties of the alloy and this is suggested to be a result of the formation of brittle sulphur compound at the grain boundaries of the alloy when the optimum concentration was exceeded.Keywords: Aluminum alloys; sand casting; microstructure; mechanical properties; optical microscopy

Preparation, characterization and evaluation of some metallic lube oil additives

All mechanical equipment suffers from wear due to the time of use and exposure to contaminants that can damage its movable parts. One way to extend the life time of this equipment is through the use of suitable lubricating oil with different additives. Detergents, especially basic detergents, contain reserve base that will neutralize the acids to form salts. While this decreases the corrosive tendency of the acids formed at high temperatures. Dispersants also disperse sludge formed in engine operated at low temperature. In the present work, different metallic detergent/dispersant additives will be prepared via reaction of dodecyl phenol with calcium hydroxide in different ratios and different amounts of sulfur. The structures of the prepared compounds were confirmed by Fourier transform infrared spectroscopy (FTIR), Proton Nuclear Magnetic Resonance (H 1 - NMR) and molecular weight is determined. All the prepared compounds were found to be soluble in lubricating oil. The efficiency of the prepared compounds as antioxidant and detergent/dispersant additives for lubricating oil was investigated. It was found that the additives have excellent power of dispersion and detergency and the efficiency as antioxidant increases by increasing the sulfur content up to 1.5% and increases by increasing the percentage of metal in the additives.

Preliminary Study on the Removal of Hexavalent Chromium in Wastewater with Reduction of Sulfur Dioxide

The paper focused on a self-developed methodology through using sulfur dioxide to deal with high concentration of chromium-containing wastewater. It studied the effects of different pH values, different reaction time, different temperatures and different amounts of sulfur with sulfur dioxide reduction reaction on the chromium-containing wastewater. The results showed that: when the reaction conditions were controlled as follows: the pH values ranged from 2 to 4, the reaction temperature was controlled 40~60°C, the amount of sulfur in theoretical was 1.2 times and the reaction time was 40 min, the hexavalent chromium in the high concentrations of chromium-containing wastewater could be effectively removed.

재배 중 황 처리 횟수가 양파의 화학적 조성 개선 및 품질 특성에 미치는 영향

양파 재배 시 국내 토양에 절대적으로 부족한 황을 처리 횟수를 달리하여 재배 생산한 후, 황 함유 성분(sulfur-containing compounds)을 포함한 양파의 화학적 조성과 물리적 관능적 특성이 개선되었는지를 평가하였다. 선행연구를 토대로, 파종 시 토양에 직접 MSM 식이 유황을 1회 공통 처리하고 수확 2달 전황을 1회만 추가 처리한 군(Sulfur-1)과 수확 3달 전부터 수확 1달 전 까지 일정 간격으로 황을 총 4회 처리한 군(Sulfur-4)으로 구별하였으며, 황을 전혀 처리하지 않은 군(Control-S)과 타 지역 양파(Control-M)를 비교를 위한 대조군으로 선정하였다. 황 처리 횟수가 증가함에 따라, 수분은 감소하는 경향을, 총 질소로 측정된 조단백질과 무기질 총량인 회분(p<0.01), 그리고 식이섬유는 증가하는 경향을 나타내었으며, Mg, K, Fe, Zn 등이 증가하여(p<0.05), 전반적으로 무기질을 포함한 화학적 조성이 개선되었음을 시사하였다. 또한, 항산화력의 지표인 총 환원물질의 양도 2배 가량 유의적으로 증가하는 결과가 관찰되었다(p<0.05). 그러나, 황 함유 성분인 thiosulfinate와 함황 아미노산에서는 황 처리 효과가 관찰되지 않았고, 전자코로 측정된 향미 프로파일 역시 향미 성분의 차이를 시사하지 않았다. 이는, 본 실험에서 처리된 황 수준은 질소대사 및 토양의 pH를 변화시키는 간접적 경로를 통한 양파의 이화학적 조성 변화는 가능하게 할 수 있었으나, 황 함유 성분들을 직접적으로 증가시키기에는 충분하지 못했음을 시사하였다. 그럼에도 불구하고, 황 처리 횟수 증가와 함께, 함황 성분들에 의해 주로 인지되는 매운 맛과 매운 향 특성은 관능적으로 강해지는 것으로 평가되었다. 이러한 차이는, 양파 특유의 냄새 성분들이 지닌 낮은 역치에서 기인한 것으로 해석하였다. 한편, Control-S, Sulfur-1, Sulfur-4 양파들은 <TEX>$4^{\circ}C$</TEX>에서 4개월 동안 저장한 후, 모두 수분의 큰 증가 없이 총 환원력이 2배 가량 증가하였으며(p<0.01), 황 처리군이 무처리군에 비해 여전히 유의적으로 높았다(p<0.001). 반면, 동일조건에서 Control-M은 유의적 변화가 관찰되지 않았다. 이러한 차이는, 황 처리, 호흡작용으로 인한 환원당의 증가 이외에 지역적 영향이 관여했을 가능성을 시사하였다. Onions were treated with different amounts of sulfur (S) during cultivation and examined for their physicochemical properties and flavor. Onions cultivated without S application were the control group; the treatment groups were grown in soil that had been pretreated with S and received additional S applications or four times before harvest. As the number of S applications increased, the levels of crude protein, quantified with total nitrogen; ash, approximating total amounts of minerals; and dietary fiber of the onions tended to increase. The mineral compositions also improved, with noticeable increases in the levels of Mg, K, Fe, and Zn. In particular, the reducing capacity of the onions increased appreciably (p<0.05), without increases in the levels of S-containing compounds such as thiosulfinate or S-containing amino acids. Nevertheless, the spicy hot taste and flavor, which is generated mainly from S-containing compounds, were perceived more strongly in the onions that had received more S applications.

Effect of sulfur and copper amounts in sol–gel precursor solution on the growth, crystal properties, and optical properties of Cu2ZnSnS4 films

Cu2ZnSnS4 (CZTS) thin films were deposited by sol–gel spin coating using precursor solutions prepared with copper acetate, zinc acetate, tin chloride, and thiourea in methanol and ethylenediamine followed by sulfurization. Sol–gel precursor solutions were prepared with different amounts of sulfur and copper, and their effects on film growth, crystal properties, and optical properties of CZTS films were investigated. CZTS film thickness increased with the amount of metal salt in the precursor solution. This is attributed to an increase in solution viscosity and a decrease in the solution density/viscosity ratio. All CZTS thin films exhibited kesterite structures with absorption coefficients larger than 104 cm−1 in the visible region. Band gap energy increased with increasing amounts of sulfur and decreasing amounts of copper. The blue shift of the band gap is attributed to changes in the degree of p–d hybridization related to Cu d- and S p-levels. The role of sulfur and copper on Hall mobility and carrier concentration was investigated. By optimizing the metal salt ratio in the precursor, CZTS film with a resistivity of 5.3 × 10−2 Ωcm were prepared.

Np(V) reduction by humic acid: Contribution of reduced sulfur functionalities to the redox behavior of humic acid

The role of sulfur-containing functional groups in humic acids for the Np(V) reduction in aqueous solution has been studied with the objective to specify individual processes contributing to the overall redox activity of humic substances. For this, humic acid model substances type M1-S containing different amounts of sulfur (1.9, 3.9, 6.9wt.%) were applied. The sulfur functionalities in these humic acids are dominated by reduced-sulfur species, such as thiols, dialkylsulfides and/or disulfides. The Np(V) reduction behavior of these humic acids has been studied in comparison to that of the sulfur-free humic acid type M1 at pH 5.0, 7.0 and 9.0 under anaerobic conditions by means of batch experiments. For Np redox speciation in solution, solvent extraction and ultrafiltration were applied. In addition, redox potentials of the sample solutions were monitored. At pH 5.0, both rate and extent of Np(V) to Np(IV) reduction were found to increase with increasing sulfur content of the humic acids. At pH 7.0 and 9.0, sulfur functional groups had only a slight influence on the reduction behavior of humic acid toward Np(V). Thus, in addition to quinoid moieties and non-quinoid phenolic OH groups, generally acknowledged as main redox-active sites in humic substances, sulfur functional groups have been identified as further redox-active moieties of humic substances being active especially in the slightly acidic pH range as shown for Np(V). Due to the low sulfur content of up to 2wt.% in natural humic substances, their contribution to the total reducing capacity is smaller than that of the other redox-active functional groups.