Green‐light emission through energy transfer from Ce3+ to Tb3+ ions in the Li2SO4–Al2(SO4)3 system

An energy transfer process from Ce³⁺ to Tb³⁺ ions was successfully achieved in a Li₂SO₄–Al₂(SO₄)₃ mixed‐sulphate system. A wet‐chemical synthesis was employed to prepare the Li₂SO₄–Al₂(SO₄)₃ system by doping Ce³⁺ and Tb³⁺ ions individually as well as collectively. The phases were identified using X‐ray diffraction studies. The as‐prepared samples were characterized by FT‐IR and photoluminescence measurements. Green‐light emission was exhibited by Ce³⁺, Tb³⁺ co‐doped Li₂SO₄–Al₂(SO₄)₃ system, thus, indicating its potential as a material for display devices or in the lamp industry.     

Dy(3+) and Mn(2+) emission in fluoride- and chloride-based Na(3) (SO(4) )X (X = F or Cl) phosphors

In the present study, Na₃(SO₄)X (X = F or Cl) halosulphate phosphors have been synthesized by the solid‐state diffusion method. The phase formation of the compounds Na₃(SO₄)F and Na₃(SO₄)Cl were confirmed by X‐ray powder diffraction (XRD) measurement. Photoluminescence (PL) excitation spectrum measurement of Na₃(SO₄)F:Ce³⁺ and Na₃(SO₄)Cl:Ce³⁺ shows this phosphor can be efficiently excited by near‐ultraviolet (UV) light and presents a dominant luminescence band centred at 341 nm for Ce³⁺, which is responsible for energy transfer to Dy³⁺and Mn²⁺ ions. The efficient Ce³⁺ → Dy³⁺ energy transfer in Na₃(SO₄)F and Na₃(SO₄)Cl under UV wavelength was observed due to ⁴ F_9/2 to ⁶H_15/2 and ⁶H_13/2 level, while Ce³⁺ → Mn²⁺ was observed due to ⁴ T₁ state to ⁶A₁. The purpose of the present study is to develop and understanding the photoluminescence properties of Ce³⁺‐, Dy³⁺‐ and Mn²⁺‐doped fluoride and chloride Na₃(SO₄)X (X = F or Cl) luminescent material, which can be the efficient phosphors in many applications, such as scintillation applications, TL dosimetry and the lamp industry, etc. Copyright © 2012 John Wiley & Sons, Ltd.     

Novel red colour emitting Ca0.995Mg2(SO4)3:0.5Eu2+ phosphor under ultraviolet,blue, and green excitation for plant growth LEDs

In the recent few years, Eu²⁺- and Mn⁴⁺-activated phosphors are widely used as potential colour converters for indoor plant cultivation lighting application due to their marvellous luminescence characteristics as well as low cost. In this investigation, we synthesized novel red colour-emitting Ca_(2−x)Mg₂(SO₄)₃:xmol% Eu²⁺ (x = 0–1.0 mol%) phosphors via a solid-state reaction method in a reducing atmosphere. The photoluminescence (PL) excitation spectra of synthesized phosphors exhibited a broad excitation band with three excitation bands peaking at 349 nm, 494 nm, and 554 nm. Under these excitations, emission spectra exhibited a broad band in the red colour region at ~634 nm. The PL emission intensity was measured for different concentrations of Eu²⁺. The maximum Eu²⁺ doping concentration in the Ca₂Mg₂(SO₄)₃ host was observed for 0.5 mol%. According to Dexter theory, it was determined that dipole–dipole interaction was responsible for the concentration quenching. The luminous red colour emission of the sample was confirmed using Commission international de l'eclairage colour coordinates. The results of PL excitation and emission spectra of the prepared phosphors were well matched with excitation and emission wavelengths of phytochrome P_R. Therefore, from the entire investigation and obtained results it was concluded that the synthesized Ca_0.995Mg₂(SO₄)₃:0.5mol%Eu²⁺ phosphor has huge potential for plant cultivation application.     

Luminescence of Eu and Ce in K3Ca2(SO4)3F fluoride material

A new halophosphor K₃Ca₂(SO₄)₃ F activated by Eu or Ce and K₃Ca₂(SO₄)₃ F:Ce,Eu co‐doped halosulfate phosphor has been synthesized by the co‐precipitation method and characterized for its photoluminescence (PL). The PL emission spectra of the K₃Ca₂(SO₄)₃ F :Ce phosphor show emission at 334 nm when excited at 278 nm due to 5d → 4f transition of Ce³⁺ ions. In the K₃Ca₂(SO₄)₃ F:Eu lattice, Eu²⁺ (440 nm) as well as Eu³⁺ (596 nm and 615 nm) emissions have been observed showing ⁵D₀ → ⁷ F₁ and ⁵D₀ → ⁷ F₂ transition of the Eu³⁺ ion, which is in the blue and red region of the visible spectrum respectively. The trivalent europium ion is very useful for studying the nature of metal coordination in various systems owing to its non‐degenerate emitting ⁵D₀ state. K₃Ca₂(SO₄)₃ F:Ce,Eu is suitable for Ce³⁺ → Eu²⁺ → Eu³⁺ energy transfer in which Ce³⁺and Eu²⁺ play the role of sensitizers and Eu²⁺ and Eu³⁺ act as the activators. The observations presented in this paper are relevant for lamp phosphors. Copyright © 2015 John Wiley & Sons, Ltd.     

Are Sulfurous Soil Amendments (S0, Fe(II)SO4, Fe(III)SO4) an Effective Tool in the Restoration of Heathland and Acidic Grassland after Four Decades of Rock Phosphate Fertilization?

This paper deals with the complex issue of reversing long‐term improvements of fertility in soils derived from heathlands and acidic grasslands using sulfur‐based amendments. The experiment was conducted on a former heathland and acid grassland in the U.K. that was heavily fertilized and limed with rock phosphate, chalk, and marl. The experimental work had three aims. First, to determine whether sulfurous soil amendments are able to lower pH to a level suitable for heathland and acidic grassland re‐creation (approximately 3 pH units). Second, to determine what effect the soil amendments have on the available pool of some basic cations and some potentially toxic acidic cations that may affect the plant community. Third, to determine whether the addition of Fe to the soil system would sequester PO₄^? ions that might be liberated from rock phosphate by the experimental treatments. The application of S⁰ and Fe^(II)SO₄^? to the soil was able to reduce pH. However, only the highest S⁰ treatment (2,000 kg/ha S) lowered pH sufficiently for heathland restoration purposes but effectively so. Where pH was lowered, basic cations were lost from the exchangeable pool and replaced by acidic cations. Where Fe was added to the soil, there was no evidence of PO₄^? sequestration from soil test data (Olsen P), but sequestration was apparent because of lower foliar P in the grass sward. The ability of the forb Rumex acetosella to apparently detoxify Al³⁺, prevalent in acidified soils, appeared to give it a competitive advantage over other less tolerant species. We would anticipate further changes in plant community structure through time, driven by Al³⁺ toxicity, leading to the competitive exclusion of less tolerant species. This, we suggest, is a key abiotic driver in the restoration of biotic (acidic plant) communities.     

Enhanced luminescence and white light emission from Eu3+‐co‐doped K3Ca2(SO4)3Cl:Dy3+ phosphor with near visible ultraviolet excitation for white LEDs

The luminescent properties of europium (Eu)‐ and dysprosium (Dy)‐co‐doped K₃Ca₂(SO₄)₃Cl halosulfate phosphors were analyzed. This paper reports the photoluminescence (PL) properties of K₃Ca₂(SO₄)₃Cl microphosphor doped with Eu and Dy and synthesized using a cost‐effective wet chemical method. The phosphors were characterized by X‐ray diffraction and scanning electron microscopy. The CIE coordinates were calculated to display the color of the phosphor. PL emission of the prepared samples show peaks at 484 nm (blue), 575 nm (yellow), 594 nm (orange) and 617 nm (red). The emission color of the Eu,Dy‐co‐doped K₃Ca₂(SO₄)₃Cl halophosphor depends on the doping concentration and excitation wavelength. The addition of Eu in K₃Ca₂(SO₄)₃Cl:Dy greatly enhances the intensity of the blue and yellow peaks, which corresponds to the ⁴ F_9/2 → ⁶H_15/2 and ⁴ F_9/2 → ⁶H_13/2 transitions of Dy³⁺ ions (under 351 nm excitation). The Eu³⁺/Dy³⁺ co‐doping also produces white light emission for 1 mol% of Eu³⁺, 1 mol% of Dy³⁺ in the K₃Ca₂(SO₄)₃Cl lattice under 396 nm excitation, for which the calculated chromaticity coordinates are (0.35, 0.31). Thus, K₃Ca₂(SO₄)₃Cl co‐doped with Eu/Dy is a suitable candidate for NUV based white light‐emitting phosphors technology. Copyright © 2014 John Wiley & Sons, Ltd.     

Luminescence characteristics of Na3Ca2(SO4)3F: Ce3+ fluoride material

A new Na₃Ca₂(SO₄)₃F: Ce³⁺ phosphor synthesized by a solid state diffusion method is reported. The photoluminescence study showed a single high intensity emission peak at 307 nm wavelength when excited by UV light of wavelength 278 nm. An unresolved peak of comparatively less intensity was also observed at 357 nm along with the main peak. The characteristic emission of dopant Ce in Na₃Ca₂(SO₄)₃F phosphor clearly indicated that it resides in the host lattice in trivalent form. The emission peak can be attributed to 5d → 4f transition of rare earth Ce³⁺. The prepared sample is also characterized for its thermoluminescence properties. The TL glow curve of prepared sample showed a single broad peak at 147°C. The trapping parameters are also evaluated by Chen's method. The values of trap depth (E) and frequency factor (s) were found to be 0.64 ± 0.002 eV and 1.43 × 10⁷ s^–1 respectively. The study of PL and TL along with evaluation of trapping parameters has been undertaken and discussed for the first time. Copyright © 2014 John Wiley & Sons, Ltd.     

Availability of Ca from Ca45SO4 in a highly saline-sodic soil

Summary Application of gypsum (tagged Ca⁴⁵SO₄.2H₂O) caused a considerable increase in dry matter yield and content of Ca, Ca⁴⁵, Mg and K and Ca:Na and (Ca+Mg): (Na+K) ratios and a decrease in the content of Na, N and P in dhaincha tops. There was a considerable increase in the total uptake of Ca, Mg, Na, K, N, P and Ca⁴⁵ by plant tops in response to gypsum. Contribution of Ca from applied Ca⁴⁵SO₄ varied from 78.3 to 84.7 per cent of the total Ca in plant tops, whereas, its uptake from this source varied from 52.18 to 98.73 me per 100 g plant tops. re]19720705     

Catalytic effect of water,water dimer,HCOOH and H2SO4 on the isomerisation of HON(O)NNO2 to ON(OH)NNO2: a mechanism study

ABSTRACT

In this article, we report a theoretical investigation on the role of several catalysts in the isomerisation mechanisms of HON(O)NNO₂ to ON(OH)NNO₂ by theoretical method of CBS-QB3. The isomerisation reactions with catalyst X (X?=?H₂O, (H₂O)₂, HCOOH and H₂SO₄) are multi-hydrogen atom transfer reactions. Compared to the isomerisation mechanisms and rate constant of HON(O)NNO₂ to ON(OH)NNO₂ without catalysts, incorporation of the catalyst X shows different positive catalytic effects on affecting the reaction processes, with the H₂SO₄-assisted reaction being the most favourable. Such different catalytic effects are mainly related to the size of the ring structure in X-assisted transition states and the different values of pK_a and proton affinities for HCOOH and H₂SO₄. Besides, compared with the barrier height of the isomerisation process from HON(O)NNO₂ to ON(OH)NNO₂ with HN(NO₂)₂ and HON(O)NNO₂, the barrier of H₂SO₄-assisted reaction is lower by 9.3 and 4.5?kcal?·mol^?1, meanwhile, the rate constant of H₂SO₄ catalyzed is larger than water and water dimer–assisted by 3–5 and 2–3 orders of magnitude, respectively. So, H₂SO₄-assisted reaction is the most favourable.     

Ecology of SO2 resistance: III. Metabolic changes of C3 and C4 Atriplex species due to SO2 fumigations

Summary The photosynthetic processes of two ecologically-matched, herbaceous Atriplex species differed in their response to SO₂ fumigations. Atriplex triangularis, a C₃ species, was more sensitive than the C₄ species, A. sabulosa. This difference in sensitivity can be attributed in part to the higher conductance of the C₃ species in normal air and saturating light as well as greater stimulation of stomatal opening following exposure to SO₂. In addition, photosynthetic mechanisms of the C₃ species had higher intrinsic SO₂ sensitivity than the C₄ species. Differences between photosynthetic responses of these two species may also reflect differences in morphological configuration of mesophyll tissues and greater SO₂ sensitivity of the initial photosynthetic carboxlating enzyme of the C₃ species. It is likely that certain of the differences in photosynthetic SO₂ sensitivity of these contrasting C₃ and C₄ Atriplex species are characteristic of C₃ and C₄ plants in general.Abbreviations PEP carboxylase phosphoenolpyruvate carboxylase - RuBP carboxylase ribulose-1,5-bisphosphate carboxylase     

Photoluminescence in K3Ca2(SO4)3Cl‐doped Eu3+ phosphor

In this article we report Eu³⁺ luminescence in novel K₃Ca₂(SO₄)₃Cl phosphors prepared by wet chemical methods. The Eu³⁺ emission was observed at 594 nm and 615 nm, keeping the excitation wavelength constant at 396 nm nearer to light‐emitting diode excitation, Furthermore, phosphors were characterized by X‐ray diffraction for the confirmation of crystallinity. The variation of the photoluminescence intensity with impurity concentration has also been discussed. Thus, prominent emission in the red region makes prepared phosphors more applicable for white light‐emitting diodes. Copyright © 2013 John Wiley & Sons, Ltd.     

Efficiency of HCl- and H2SO4- acidulated rock phosphates for rice (Oryza Sativa L.) on acid soils

Summary Rock phosphates from Udaipur (India), North Carolina, Florida, Tennessee and Missouri (USA) were acidulated with HCl or H₂SO₄, to the extent of 25, 50, 75 or 100 per cent of the requirement for complete conversion into single superphosphate. Partial acidulation resulted in the formation of a mixture of water- and citrate-soluble and -insoluble phosphates, the proportion of the first two increasing with increasing degree of acidulation, at the expense of the insoluble phosphate. For a given degree of acidulation, the P compounds formed with HCl or H₂SO₄ were of comparable composition, except that the HCl-acidulated products were hygroscopic. Pot experiments with acid P-deficient soils showed that the behaviour of the HCl- or H₂SO₄- acidulated products in respect of P availability in soil, grain yield response and P uptake by rice was more or less similar. Partially acidulated rock phosphate to the extent of 50 per cent with either of the acids was found to be suitable for growing rice under flooded soil conditions. There is thus scope for the use of HCl- acidulated rock phosphate as a substitute for the H₂SO₄- acidulated product, for growing rice in acid soils. The scope for use of lower degree HCl-acidulated product in an upland crop — rice rotation in acid soils is also discussed.     

Effect of Dy3+ or Eu2+ co‐activator on a BaCa(SO4)2:Ce3+ mixed alkaline earth sulfate phosphor

The individual emission and energy transfer between Ce³⁺ and Eu²⁺ or Dy³⁺ in BaCa(SO₄)₂ mixed alkaline earth sulfate phosphor prepared using a co‐precipitation method is described. The phosphor was characterized by X‐ray diffraction (XRD) and photoluminescence (PL) studies and doped by Ce;Eu and Dy rare earths. All phosphors showed excellent blue–orange emission on excitation with UV light. PL measurements reveal that the emission intensity of Eu²⁺ or Dy³⁺ dopants is greater than when they are co‐doped with Ce³⁺. An efficient Ce³⁺ → Eu²⁺ [²T_2g(4f⁶5d) → ⁸S_7/2(4f₇)] and Ce³⁺ → Dy³⁺ (⁴ F_9/2 → ⁶H_15/2 and ⁴ F_9/2 → ⁶H_13/2) energy transfer takes place in the BaCa(SO₄)₂ host. A strong blue emission peak was observed at 462 nm for Eu²⁺ ions and an orange emission peak at 574 nm for Dy³⁺ ions. Hence, this phosphor may be used as a lamp phosphor. Copyright © 2015 John Wiley & Sons, Ltd.     

Photosynthetic and growth response to fumigation with SO2 at elevated CO2 for C3 and C4 plants

Summary Six early successional plant species with differing photosynthetic pathways (3 C₃ species and 3 C₄ species) were grown at either 300, 600, or 1,200 ppm CO₂ and at either 0.0 or 0.25 ppm SO₂. Total plant growth increased with CO₂ concentration for the C₃ species and varied only slightly with CO₂ for the C₄ species. Fumigation with SO₂ caused reduced growth of the C₃ species at 300 ppm CO₂ but not at the higher concentrations of CO₂. Fumigation with SO₂ reduced growth of the C₄ species at high CO₂ and increased growth at 300 ppm CO₂. Leaf area increased with increasing CO₂ for all plant species. Fumigation with SO₂ reduced leaf area of C₃ plants more at low CO₂ than at high CO₂ while leaf area of C₄ plants was reduced more at high CO₂ than at low CO₂. These results support the notion that C₃ species are more sensitive to SO₂ fumigation than are C₄ species at concentrations of CO₂ equal to that found in normal ambient air. However, the difference in sensitivity to SO₂ between C₃ and C₄ species was found to be reversed at higher concentrations of CO₂. A possible explanation for this reversal based upon differences in stomatal response to elevated CO₂ between C₃ and C₄ species is discussed.     

Green synthesis,structure feature and energy transfer of yellow-emitting (Y,Gd)2O2SO4:Dy phosphors

A green chemical precipitation route was used to yield a hydrated basic sulfate precursor upon calcination at 1000°C into a series of (Y,Gd)₂O₂SO₄:Dy particles. The phosphors exhibited characteristic Dy³⁺ emissions from ⁴F_9/2→⁶H_J (J = 15/2, 13/2, 11/2) transitions under ultraviolet light excitation; the quenching concentration of Dy³⁺ was determined to be 2.5 at.%. Substitution of Gd³⁺ for Y³⁺ led to an additional strong sharp band at ~277 nm (⁸S_7/2→⁶I_J transition of Gd³⁺) in the photoluminescence excitation spectra, upon which the (Gd_0.975Dy_0.025)₂O₂SO₄ phosphor achieved a ~2.8-fold higher photoluminescence intensity via an effective energy transfer from Gd³⁺ to Dy³⁺ compared with the 354 nm excitation of Dy³⁺. Both the photoluminescence and photoluminescence excitation intensities of (Y,Gd)₂O₂SO₄:Dy phosphors increased with rising Gd³⁺ concentration and calcination temperature in the range 750–1000°C. A higher Gd³⁺ concentration slightly prolonged the effective fluorescence lifetime.     

Luminescence in Li3Al2(PO4)3:Eu2+

A series of efficient Li₃Al₂(PO₄)₃:Eu²⁺ novel phosphors were synthesized by the facile combustion method. The effects of dopant on the luminescence behavior of Li₃Al₂(PO₄)₃ phosphor were also investigated. The phosphors were characterized by X‐ray diffraction, field emission scanning electron microscope and photoluminescence techniques. The result shows that all samples can be excited efficiently by near‐ultraviolet excitation under 310 nm. The emission was observed for Li₃Al₂(PO₄)₃:Eu²⁺ phosphor at 425 nm, which corresponded to the d → f transition. The concentration quenching of Eu²⁺ was observed in Li₃Al₂(PO₄)₃:Eu²⁺ when the Eu concentration was at 0.5 mol%. The prepared powders exhibited intense blue emission at the 425 nm owing to the Eu²⁺ ion by Hg‐free excitation at 310 nm (i.e., solid‐state lighting excitation). Consequently, the availability of such a phosphor will significantly help in the development of blue‐emitting solid‐state lighting applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Modelling anion amelioration of aluminium phytotoxicity

There is good evidence for the ameliorating effect of SO₄ ^2- and F^- on the expression of Al phytotoxicity in acidic solutions. The role of OH^-, in both shifting Al speciation towards hydroxy-Al species and decreasing activities of H⁺ with increasing pH, is still controversially discussed. Grauer and Horst (1992) proposed a model based on the assumption that Al phytotoxicity is a function of the Al saturation (AlS) of exchange sites in the root apoplast and analyzed the predictions of the model in the case of cation amelioration, with special emphasis on H⁺. In this study the model is further developed by considering, in addition to Al³⁺, the complexation of Al with the anions OH^-, F^-, SO₄ ^2-, and Cl^- to form potentially toxic Al species. Association constants of these Al complexes with a ligand (L ^-) which is assumed to simulate the cation exchange sites in the root apoplast, were estimated. Affinity factors for binding to L ^- compared to Al³⁺ were derived from these estimated association constants, and values were, in a first approach, 0.79 for AlOH²⁺, 0.02 for Al(OH)₂ ⁺, and 0.13 for Al(OH)₃ ⁰ (or 0.03 choosing another hydrolysis constant). High toxicity of Al₁₃ (AlO₄Al₁₂(OH)₂₄(H₂O)₁₂ ⁷⁺) could be explained by diminished H⁺ amelioration and a high association constant to L ^-. From estimated association constants for Al-Cl complexes, low affinity factors for L ^- for these complexes were derived. Since the formation of these Al-Cl complexes is not favoured, Cl^- is predicted to have very little ameliorating effect. In the case of SO₄ ^2– and F^- complexes with Al, the derived affinity factors never exceeded 0.05 and, since formation of these complexes is favoured by high association constants, are thus in agreement with experimental results on ameliorating effects. The ranking of the anions for ameliorative effectiveness was estimated to be in the order of OH^->F^->SO₄ ^2–>Cl^-. Hydroxy amelioration in this context is restricted to the speciation effect, which is only significant above pH 4.     

Impact of ligand environment on optical,luminescence and thermometric behavior of A3(PO4)2:Sm3+ (A = Ca,Sr) phosphors

The present study investigates the impact of the ligand environment on the luminescence and thermometric behavior of Sm³⁺ doped A₃(PO₄)₂ (A = Sr, Ca) phosphors prepared by combustion synthesis. The structural and luminescent properties of Sm³⁺ ions in the phosphate lattices were investigated using powder X-ray diffraction (PXRD) and photoluminescence (PL) techniques. PXRD results of the synthesized phosphors exhibit the expected phases that are in agreement with their respective standards. Fourier-transform infrared (FTIR) spectroscopy confirms the presence of PO₄ vibrational bands. Upon excitation with near ultraviolet light, the PL studies indicated that Sr₃(PO₄)₂:Sm³⁺ phosphors exhibit a yellow light emission, whereas Ca₃(PO₄)₂:Sm³⁺ phosphors exhibit an emission of orange light. The PL emission results are in accordance with the CIE coordinates, with the Sr₃(PO₄)₂:Sm³⁺ phosphors showing coordinates of (0.56, 0.44), and the Ca₃(PO₄)₂:Sm³⁺ phosphors displaying coordinates of (0.60, 0.40). Thermal analysis shows improved stability of Ca₃(PO₄)₂:Sm³⁺ based on lower weight reduction in thermogravimetric analysis. The effect of temperature on the luminescence properties of the phosphor has been examined upon a 405 nm excitation. By using the fluorescence intensity ratio (FIR) method, the temperature responses of the emission ratios from the Sm³⁺: the ⁴F_3/2 → ⁶H_5/2 transition to the ⁴G_5/2 → ⁶H_7/2 and ⁴F_3/2 → ⁶H_5/2 transition to the ⁴G_5/2 → ⁶H_9/2 emissions are characterized. The Ca₃(PO₄)₂:Sm³⁺ phosphors are more sensitive as compared with the Sr₃(PO₄)₂:Sm³⁺ phosphors. The earlier research findings strongly indicate that these phosphors hold great promise as ideal candidates for applications in non-invasive optical thermometry and solid-state lighting devices.     

Long-term effects of SO2 on plants,SO2 metabolism and regulation of intracellular pH

The impact of SO₂ on the ionic balance of plants and its implications for intracellular pH regulation was studied to find explanations for long-term effects of SO₂. When sulphur, taken up as SO₂ by the shoots of plants, is not assimilated in organic compounds, but stored as sulphate, an equivalent amount of H⁺ is produced. These H⁺ ions are not buffered chemically, but removed by metabolic processes.On the basis of knowledge on metabolic buffering mechanisms a conceptual model is proposed for the removal of shoot-generated H⁺ by (i) OH^- ions, produced in the leaves when sulphate and nitrate are assimilated in organic compounds and/or by (ii) OH^- ions produced by decarboxylation of organic anions (a biochemical pH stat mechanism). The form in which nitrogen is supplied largely determines the potential of the plant to neutralize H⁺ in the leaves during SO₂ uptake by the proposed mechanisms.In field experiments with N₂ fixing Vicia faba L. crops, the increase of sulphate in the shoots of SO₂-exposed plants was equivalent in charge to the decrease of organic anion content, calculated as the difference between inorganic cation content (C) and inorganic anion content (A), indicating that H⁺ ions produced in the leaves following SO₂ uptake were partly removed by OH^- from sulphate reduction and partly by decarboxylation of organic anions.The appearance of chronic SO₂ injury (leaf damage) in the field experiment at the end of the growing period is discussed in relation to the impact of SO₂ on the processes involved in regulation of intracellular pH. It is proposed that the metabolic buffering capacity of leaf cells is related to the rates of sulphate and nitrate reduction and the import rate of organic anions, rather than to the organic anion content in the vacuoles of the leaf cells.     

Surface area and porosity of acid hydrolyzed cellulose nanowhiskers and cellulose produced by Gluconacetobacter xylinus

The physical parameters of cellulose such as surface area and porosity are important in the development of cellulose composites which may contain valuable additives which bind to cellulose. In this area, the use of acid hydrolyzed nano-dimensional cellulose nanowhiskers (CNWs) has attracted significant interest, yet the surface area and porosity of these materials have not been explored experimentally. The objective of this work was to characterize the surface area and porosity of CNWs from different origins (plant cotton/bacterium Gluconacetobacter xylinus) and different acid treatments (H₂SO₄/HCl) by N₂ adsorption; as well as to compare surface area and porosity of bacterial cellulose synthesized by static and agitated cultures. Our results showed that CNWs produced from H₂SO₄/HCl exhibited significantly increased surface area and porosity relative to starting material cotton fiber CF11. Micropores were generated in HCl hydrolyzed CNWs but not in H₂SO₄ hydrolyzed CNWs. Bacterial CNWs exhibited larger surface area and porosity compared to plant CNWs. Cellulose synthesized by G. xylinus ATCC 700178 from agitated cultures also exhibited less surface area and porosity than those from static cultures.