Strong Inorganic Acid Research Articles

Bioactivity of chitosan nanoparticles synthesized by a novel route towards Escherichia coli and Bacillus subtilis

Chitosan nanoparticles (CSNP) with an average size of 25.67 nm were synthesized via a novel wet chemical route and characterized using scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy. Comparative antibacterial assays of Chitosan NP suspensions prepared in water (at neutral pH) and in dilute acetic acid and chitosan gel prepared in dilute acetic acid/hydrochloric acid (all at concentrations up to 1%) were performed against Escherichia coli ( E. coli) and Bacillus subtilis ( B. subtilis) bacteria using spread plate method. A parallel viability test was conducted to confirm the presence of surviving cells in the bulk test volume. Minimum bactericidal concentration (MBC) of chitosan gel was 0.5 mg/ml for the bulk chitosan dissolved in 0.05% v/v aq. acetic acid and 0.1 mg/ml for chitosan dissolved in 0.01% v/v aqueous (aq.) hydrochloric acid. In comparison, Chitosan NP were found to be growth promoter at neutral pH and exhibited cell protective efficacy in presence of aq. acetic acid. The biocidal activity of chitosan gel in acidic media was higher when prepared in strong inorganic acid, that is, aq. HCl in comparison with the gel prepared in a relatively weak organic acid that is, aq. CH3COOH at the same concentration. Antibacterial action also showed pH dependence with higher activity at lower pH. However, respective aq. acids also gave comparable bactericidal action; indicating that chitosan may not have any inherent antibacterial property and basically it acts as a growth promoter.

ALIGNMENT OF FINGERING PATTERN INDUCED BY AN INTERFACIAL NEUTRALIZATION REACTION

In this paper, we numerically study buoyancy-driven chemoconvective instabilities in a vertically oriented Hele-Shaw cell. At the beginning, the cavity is filled with a homogeneous aqueous solution of a strong inorganic alkali, and this system is statically stable. We assume that the upper boundary is free, and a fixed value of the concentration of a strong inorganic acid is set there. After bringing the reactants into contact, density stratification quickly becomes unstable due to a neutralization reaction, resulting in density fingering. The mathematical model includes the effect of producing a new amount of solvent (water). We show that this effect is a reason for the sudden alignment of salt fingers that we previously observed in experiments. In this work, we carry out a formal parametric study of the system with a change in the dimensionless parameter responsible for the intensity of water production. One can interpret this variation as a sequential consideration of substances from the homologous series of alkalis. We show that there exists a critical value of the parameter, crossing which one can observe a spontaneous transition from an irregular fingering pattern to cellular chemoconvection. The latter looks like a system of fingers tightly pressed against each other with tips aligned along a horizontal line. The lower boundary of the vortices uniformly moves down. We found that instead of the usual coarsening of the structure, one observes an increase in the aspect ratio of vortices. We investigate the dynamics of the lower boundary of the fingering pattern and changes in the pattern wavelength. Complex rearrangements of the reaction front, which include the processes of plume creation and coalescence, are illustrated using space-time diagrams.

Sustainable Recovery, Surface Chemical Engineering, and Upcycling of Spent Graphite into Dual-Ion Battery

Recycling has become an absolute necessity. Spent Lithium-ion batteries (LIBs) are hazardous waste but a potential source of purified minerals. The industrial focus on LIB recycling is mostly centered on costly and scarce cathode materials recovery. Graphite is often overlooked as it fails to generate useful revenue. Herein, the waste LIBs are recycled following an all-components-recovery route that minimizes cross-contamination. However, the surface of the recovered graphite is covered with solid electrolyte interphase (SEI) formed during its first life application. Solvent wash followed by thermal treatment revives graphite for second-life applications. Three important things to consider here are the interaction of solvent media with the preformed SEI, the role of leftover SEI in forming the second-life SEI, and the effect of regenerated SEI on second-life electrochemistry. Therefore, the nature of the solvent plays a vital role in the overall process. Utilizing water is the go-to alternative but the obtained electrochemistry from water-washed graphite is below the mark. Organic solvent dimethyl carbonate (DMC) modifies the chemical composition of the interphase in such a way that it improves second-life electrochemistry. Strong inorganic acid HCl results in the highest carbon purity and makes recovered graphite suitable for non-electrochemical applications too. Electrochemically superior DMC-washed graphite is repurposed into a dual-ion full cell that delivers an average voltage of 4.5 V and an energy density of 110 Wh kg-1. Figure 1

Choline-Based Deep Eutectic Solvent and Microwave Irradiation as Tools for PET Identification in Blend Fabric

A new, rapid, and eco-friendly technique for identification of polyethylene terephthalate (PET) composition in blend fabric was developed. This technique could replace a conventional composition identification of PET using toxic chemicals such as halogenated organic solvent or strong inorganic acid. Choline-based deep eutectic solvents (DES), such as ethylene glycol- choline chloride, were used as a treatment medium under microwave irradiation. The PET portion of the blend fabrics, such as 65/35 and 50/50 PET/cotton was completely removed by DES containing 5% NaOH (w/v) after 100–140 s of microwave irradiation. Various instrumental analyses confirmed the removal of PET. Finally, a commercial sample was also tested as a practical application of the new test method.

Corrosion degradation behavior of PBO fibers under strong inorganic acid

Known as the super fiber of the twenty-first century, poly-p-phenylenebenzobisoxazole (PBO) fibers exhibit outstanding strength and modulus, fire and heat resistance, which are superior to those of poly-p-phenylene terephthalamide fiber. However, the poor resistance of acid corrosion is regarded as a fatal weakness, which restricts its application in complicated chemical environment. In present work, PBO fibers were exposed in strong acid solutions under different conditions, and then, surface morphology was observed by optical microscopy and scanning electron microscopy. Substantial changes in functional groups were investigated by Fourier-transform infrared (FTIR) spectroscopy, as well as changes in crystalline structure using differential scanning calorimetry (DSC) and thermal stability using thermogravimetric analysis (TGA). After treatment by H2SO4 and HNO3 solution, the strength of the fibers declines typically, while the modulus increases. It is attributed to the formation of N–H bonds in the vicinity of 3410.0 cm−1 confirmed by FTIR spectra. Hydrogen bonds, derived from N–H bonds, increase the thermal degradation temperature from 716.4 °C (untreated) to 725.6 °C (treated by H2SO4), shown in TGA curves. HNO3 treatment is more destructive than that of H2SO4. There exist longitudinal corrosion cracks after treatment by HNO3 solution. Furthermore, HNO3 solution penetrates into crystalline region and destroys the ordered crystal structure of PBO fibers demonstrated by DSC results.

Incinerated Sewage Sludge Bottom Ash- Chemical processing, Leaching patterns and Toxicity testing

Sewage sludge bottom ash, which is the major fraction obtained from the incineration of sewage sludge was treated with various organic and inorganic acids for heavy metal removal, along with a comparative phosphate treatment for heavy metal fixation. Malonic acid, an organic acid, was found to remove heavy metals better as compared to nitric acid, a strong inorganic acid. The acid treated samples were further examined for heavy metal leaching, followed by marine toxicity/abnormality testing of the leachates, where acid treated and phosphate treated ash leachate displayed higher (with malonic acid proving to be most toxic) and similar toxicity profiles as compared to raw ash leachate respectively. Raw ash was tested for its leaching patterns at different liquid/solid ratios(L/S = 5 and 10), salinities and time points (24, 48 and 72 h), where the leaching was found to saturate at L/S = 5 and at 24 h with varied salinity effecting the leaching insignificantly. When raw ash was benchmarked against concrete sand for marine toxicity, a material commonly used for land reclamation, acute toxicity patterns were found to be mostly similar except in case of the sea urchin embryonic assay, where toxicity was detected, indicating the sensitivity of the assay to residual levels of heavy metals. The raw ash was also tested against human cell lines where it displayed size and dose-dependent toxicity. To enable the use of ash for environment applications such as coastal reclamation, appropriate treatments are required to minimize leaching of potential harmful contaminants and this study demonstrates the importance of post-treatment of ash on its subsequent toxicity to organisms.

Recovery of succinic acid by integrated multi-phase electrochemical pH-shift extraction and crystallization

This work presents a novel approach for the recovery of succinic acid from aqueous solutions by electrochemically induced extraction and crystallization. The suggested process allows purification by electrical energy via pH-shift downstream operations. Experimental results show that direct electrochemical extraction can recover succinic acid from aqueous solution containing approximately 50 g/L succinic acid at bulk pH of 5–7 without prior acidification by strong inorganic acid. Simultaneously, an alkaline solution was obtained from the cathode reaction, which can potentially reduce the base consumption for pH maintenance in succinic acid fermentation. Replacing salt waste generating base and acid addition by electrochemically operated pH-shift unit operations can provide more environmentally benign separation strategies for the production of bio-based succinic acid. Experimental examples for electrochemical extraction, back-extraction and crystallization are given. For extraction and back-extraction, a faradaic efficiency of 22–36% was recorded. Crystal size distribution of succinic acid from electrochemical crystallization was found to be comparable to commercially available succinic acid. Based on the experimental results we suggest a concept for the recovery of solid succinic acid from aqueous solution and pH-control in fermentation by a series of four electrochemical downstream operations, which can be coupled into two electrochemical cells. This process layout enables operating fermentation at optimal pH for maximal space-time-yield and independent pH-shift separation in the downstream, while product losses can be minimized by closed recycle streams. In the long-term perspective, electrochemical unit operations provide a way to utilize electricity for the purification of carboxylic acids.

A Putative Adverse Outcome Pathway Relevant to Carcinogenicity Induced by Sulfuric Acid in Strong Inorganic Acid Mists.

Based on epidemiological studies, an International Agency for Research on Cancer Working Group determined that strong inorganic acid mists containing sulfuric acid are carcinogenic to human even though, sulfuric acid, per se, is not. Accumulative studies indicate that there is a link between chronic occupational exposure to sulfuric acid mists and an increased risk of laryngeal cancer. Unintended, acute exposure to sulfuric acid mists can cause corrosive damage to target tissues depending on the route of exposure. This review compares the toxicity and carcinogenicity of sulfuric acid mists compared to other strong inorganic acid mists. It also examines the routes and duration of exposure (short-term, prolonged, and long-term). In vivo evidence does not support or refute the carcinogenicity of sulfuric inorganic mists even though its co-carcinogenic or promoting potential has been considered. On the basis of existing evidence on sulfuric acid mist toxicity, we suggested a putative adverse outcome pathway (AOP) relevant to carcinogenicity caused by mists containing sulfuric acid. A possible key factor involved in sulfuric acid mist carcinogenesis is the genotoxic effects of low pH since it can increase instability in chromosomes and DNA. A putative AOP for sulfuric acid mist carcinogenicity would help generate better risk assessments and more accurate predictions regarding the risk of developing cancer due to prolonged exposure. Establishing an AOP would also be useful for future studies examining the carcinogenicity of other strong inorganic mists.

Comparative Studies of Combined Influence of Variables on the Esterification Degree of Pectin Extracted by Sulfuric Acid and Citric Acid

The influence of extraction variables on degree of esterification (DE) of pectin was studied due to the significant effects of DE on the properties of the pectin-based functional biomaterials. The extracting agents (sulfuric acid and citric acid), pH value of extraction solution, extraction time, and temperature were selected to study the hydrolysis reaction of carboxylic acid ester by response surface methodology (RSM). The hydrolysis reaction occurred more violently in the weak organic acid solution than that in the strong inorganic acid solution. The DE was significantly influenced by pH of extraction solution, extraction time, and temperature through the analysis of variance. In addition, the values of DE reduced with the increasing of extraction temperature, lapse of time, and decreasing of pH value. What is more, the effects of extraction conditions on the yield, monosaccharide composition, content of protein, and ferulic acid were also studied. It is evident that the lower pH value contributed to higher extraction yield. The content of Total CH and GalA of pectin extracted by sulfuric acid were higher than that of pectin extracted by citric acid, and the content of monosaccharide showed an opposite trend.

The direct-current characteristics and surface repairing of a hydrogen-terminated free-standing polycrystalline diamond in aqueous solutions

As we know that more effective synthesis of diamond combined with physical and chemical properties of hydrogen termination in aqueous environment as well as device structure design can greatly facilitate the chemical and electrochemical applications of higher cost-performance diamond. For this purpose, the direct-current (DC) characteristics, surface reaction and reparation of a hydrogen-terminated DC arc jet plasma CVD polycrystalline diamond, which has a high cost-performance, were characterized by I-V experiments based on a FET-like structure device in multiple aqueous solutions. The variation trends of the I-V properties of device based on pH were similar in different aqueous solutions but could be affected by disparate ions (such as K+ ions) or organic molecules (such as citric acid radicals or a benzene ring). Especially, owing to the founded replacement of hydrogen termination with hydroxyl (OH), carboxyl radical (COOH) or carbon-oxygen bond (COC) in mixed solution, i.e., KHP + H2SO4 (and +NaOH) solutions, the resistance of the device was remarkably increased from 13.57 kΩ to 95.78 kΩ. However, the raised resistance of surface reacted diamond (SRD) can be reduced prominently by repairing hydrogen termination through negative potential sweeps (NPS) at a low negative potential (−1 to −3 V) if the SRD was introduced as an electrode in a strong inorganic acid. What's more, the NPS repaired device, which subsequently stored for four weeks, was more sensitive than the original hydrogen plasma-treated diamond in aqueous solution environments. This repaired result was coming out of NPS re-formed CH bonds with higher intensity. These findings will be the references of failure and reparation of diamond hydrogen termination in aqueous environment.

A bio-hydrometallurgical approach towards leaching of lanthanum from the spent fluid catalytic cracking catalyst using Aspergillus niger

Spent fluid catalytic cracking catalysts (SFCCC) are the wastes generated from oil refineries, which accounts for 700,000–900,000 metric ton/year worldwide. Lanthanum, a short-term near critical element is the key component of SFCCC and accounts for 8170 mg/Kg. The current research intends to recover lanthanum from SFCCC by Aspergillus niger and compare the results with strong organic and inorganic acid leaching. Batch studies of one-step bioleaching (OSB) at 1, 3 and 5% pulp densities yielded 63%, 52%, and 33% lanthanum recovery, respectively. The decrease in leaching efficiency with an increase in pulp density may be attributed to the inhibition effect of SFCCC on A. niger. Citric acid was the main lixiviant produced by A. niger, whose production was triggered by SFCCC at ≤1% pulp density. Acidic pH of the leaching medium suggested acidolysis as the key mechanism. Cell-free spent medium bioleaching (cfSMB) resulted in 30.8% leaching recovery, which was significantly less than the OSB. In chemical leaching, sulfuric and nitric acid showed 38% efficiency whereas oxalic acid showed 5% recovery. Hydrochloric, citric and gluconic acids resulted in 68%, 65%, and 64% leaching recoveries, respectively, which is nearly the same as that offered by OSB. OSB being the greener process, suggested for lanthanum leaching from SFCCC over other processes.

Caustic Hypocalcemia: Hydrofluoric Acid Burn

Hydrofluoric acid is a strong inorganic acid. It differs from other acids in that the fluoride ion readily penetrates the skin, causing destruction of deep tissue lay ers and even bone. Burns caused by hydrofluoric acid can be life-threatening. The specific antidote, calcium gluconate, can be applied topically, injected into tissue or infused intra-arterially. Emergency medical teams should be familiar with the symptoms and of hydrofluoric acid exposure and should be ready to respond properly in case of emergency. In this paper, we present a case of hydrofluoric acid poisoning due to accidental exposure to hydrofluoric acid.

Impact of acid adaptation on attachment of Listeria monocytogenes to stainless steel during long-term incubation under low or moderate temperature conditions and on subsequent recalcitrance of attached cells to lethal acid treatments

This study aimed to evaluate the possible impact of acid adaptation of Listeria monocytogenes cells on their attachment to stainless steel (SS) during long-term incubation under either low or moderate temperature conditions and on the subsequent recalcitrance of attached cells to lethal acid treatments. Initially, nonadapted or acid-adapted stationary phase L. monocytogenes cells were used to inoculate (ca. 108CFU/ml) brain–heart infusion (BHI) broth in test tubes containing vertically placed SS coupons. Incubation was carried out at either 5 or 30°C for up to 15days, under static conditions. On the 5th, 10th and 15th days of incubation, attached cells were subjected to lethal acid treatments by exposing them, for either 6 or 60min, to pH2, adjusted with either hydrochloric or lactic acid. Following the acid treatments, remaining viable cells were detached (through strong vortexing with glass beads) and enumerated by agar plating, and also indirectly quantified by conductance measurements via their metabolic activity. Results obtained from both quantification techniques, employed here in parallel, revealed that although the numbers of attached cells for nonadapted and acid-adapted ones were similar, the latter were found to present significantly (p<0.05) increased recalcitrance to all the acid treatments for both incubation temperatures and all sampling days. In addition and regardless of acid adaptation, when long (60min) acid treatments were applied, conductance measurements revealed that the weak organic lactic acid exhibited significantly (p<0.05) stronger antilisterial activity compared to the strong inorganic hydrochloric acid (at the same pH value of 2). To conclude, present results show that acid adaptation of L. monocytogenes cells during their planktonic growth is conserved even after 15days of incubation under both low and moderate temperature conditions, and results in the increased recalcitrance of their sessile population to otherwise lethal acid treatments. This “stress hardening” should be severely taken into account when acidic decontamination interventions are used to kill attached to equipment surfaces cells of this important pathogenic bacterium.

Leaching of Fluoride from Biotite Mica in Soil: Implications for Fluoride in Shallow Groundwater

Leaching of from biotite was investigated at room temperature by performing a series of short-term leach tests. The leaching of from biotite structure strongly depends on its weathering stage. Results of this study suggest that high concentration of is leached from highly weathered biotite, compared to fresh biotite. Results of dissolution experiments confirm that the organic acids in soil promote the leaching of from biotite compared to inorganic acids. Citric acid which is a week organic acid enhances leaching of from biotite structure compared to strong inorganic acid HNO3, independent of the weathering stage of biotite. Strong positive correlation between K+ and Fe2+ with in biotite treated with citric acid suggests that readily leachs into the solution through an ionic exchange and complex formation. Organic acids involve sorption and complex formation processes leading to release of into the solution. Our studies suggest that in the presence of organic acids is leached readily into water percolating through the soil. Therefore, shallow groundwater replenished by the water table may achieve high concentrations by this leaching process.

Electrokinetic extraction of heavy metals from dredged marine sediment

This study investigates the suitability of the electrokinetic process for extracting heavy metals from dredged marine sediment. Marine sediments have unique characteristics such as high alkalinity, high buffering capacity, and a large fraction of fine particles and organic contents. The target heavy metals were nickel (Ni), copper (Cu), zinc (Zn), and lead (Pb). Tap water was circulated in the anode and various processing fluids such as 0.1 M of ethylenediamine tetraacetic acid (EDTA), citric acid (CA), HNO 3, and HCl were circulated in the cathode under a constant voltage gradient of 1 V/cm for 15 days. Heavy metals were most efficiently extracted from the marine sediment with HCl, and the extraction efficiencies of Ni, Cu, Zn, and Pb were 71.5%, 68.6%, 62.4%, and 65.3%, respectively. In the case of citric acid, the extraction efficiencies of Ni, Cu, Zn, and Pb were 56.3%, 71.3%, 60.3%, and 54%, respectively. Even though HNO 3 is a strong inorganic acid like HCl, extraction efficiency was lower than of HCl because chloride forms a metal–chloride complex and the complex formation enhances desorption from sediment surface or ionization at alkaline pH. On the basis of the experimental results, we conclude that the electrokinetic process, using citric acid or HCl, is suitable for extracting heavy metals from dredged marine sediment.

A Population-Based Case-Control Study of Occupational Exposure to Acids and the Risk of Lung Cancer: Evidence for Specificity of Association

Occupational exposure to strong inorganic acid mists containing sulfuric acid has been recognized as a carcinogen (Group 1) since 1992. An augmented, secondary data analysis of a population-based case-control study of lung cancer was conducted to assess lung cancer-specific risks using 772 lung cancer cases diagnosed between 1981 and 1985. Individually matched controls--on age, gender, and borough of residence--were identified. Lifetime exposure to 10 acidic agents, including strong inorganic acids and some gases, was assessed from complete lifetime occupational histories in terms of concentration, frequency, and reliability of the various exposure assessments. Smoking-adjusted odds ratios and 95% confidence intervals were determined for overall and histology-categorized lung cancers using conditional logistic regression. No excess risk for overall lung cancer was associated with any of the acids, and effect modification by gender could not be identified. The absence of an acid lung cancer effect reinforces more recent toxicological data that suggest specificity to the larynx.

Construction of a Series of 1D and 2D Inorganic–Organic Hybrid Coordination Polymers Based on 1,1′‐Bis(propionic acid)‐2,2′‐biimidazole

The substitution reactions of cadmium or zinc nitrate and the new multifunctional ligand Pra 2 biim 2- [Pra 2 biim = 1,1'-bis(propionic acid)-2,2'-biimidazole] produce a series of coordination polymers with d 10 metal centers, namely, 1D [Cd(HPra 2 biim)(H 2 O)Cl] n ·nH 2 O (1), 1D [Cd 2 (Pra 2 biim)(H 2 O) 4 -(NO 3 ) 2 ] n (2), and 2D [Zn(HPra 2 biim)Cl]n (3) in acidic aqueous solutions. The presence of a strong inorganic acid, such as HCl, lead to the protonation of Pra 2 biim 2- as observed in polymers 1 and 3. Compounds 1 and 3 contain the doubly N,N'-biim-bridged [M 2 (μ 2 -N,N'-biim) 2 ] and compound 2 the singly bridged [M 2 (μ 2 -N,N'-biim)] as secondary building blocks that are interconnected by the propionate arms into 1D chains in 1 and 2, and into a 2D layer in 3. These d 10 metal polymers exhibit luminescent emissions that are sensitive to the coordination geometry of the metal centers.

Physiological and molecular analysis of the stress response of Saccharomyces cerevisiae imposed by strong inorganic acid with implication to industrial fermentations

This work aimed to identify the molecular mechanism that allows yeast cells to survive at low pH environments such as those of bioethanol fermentation. The industrial strain JP1 cells grown at pH 2 was evaluated by microarray analysis showing that most of the genes induced at low pH were part of the general stress response (GSR). Further, an acid-tolerant yeast mutant was isolated by adaptive selection that was prone to grow at low pH in inorganic but weak organic acid. It showed higher viability under acid-temperature synergistic treatment. However, it was deficient in some physiological aspects that are associated with defects in protein kinase A (PKA) pathway. Microarray analysis showed the induction of genes involved in inhibition of RNA and protein synthesis. The results point out that low pH activates GSR, mainly heat shock response, that is important for long-term cell survival and suggest that a fine regulatory PKA-dependent mechanism that might affect cell cycle in order to acquire tolerance to acid environment. These findings might guide the construction of a high-fermentative stress-tolerant industrial yeast strain that can be used in complex industrial fermentation processes.

RAMA stain: A fast, sensitive and less protein-modifying CBB R250 stain

SDS-PAGE and CBB staining are two of the most popular methods used for protein analysis. Although many reports that describe such staining methods have been published, these conventional protocols require several hours or days for staining and de-staining. In this study we describe a recently developed, fast and sensitive CBB staining method that utilizes the staining solution of RAMA that consists of the low-cost reagents: CBB R250, acetic acid, methanol and ammonium sulfate, and the destaining solution of water. Our method dose dependently detects 12 nanograms protein within 60 min and with a wide protein spectrum. Although the features of the dose-dependent relationship depend upon protein amounts and protein types, for most of the protein samples tested, a linear relationship was observed in the region from 12 to 330 ng. Moreover, through further washing, the detection sensitivity of protein is enhanced and reaches a maximum at 1.4 ng and then gradually decreases in the de-staining process. It has been shown recently through MS analyses that the sensitive colloidal CBB staining methods frequently result in artifactual methylations due to the strong acid and long contact during staining and the destaining processes. Such artifacts were reported to be reduced by the replacement of strong inorganic acid with acetic acid and because RAMA utilizes acetic acid and is in contact with the proteins for a short time during staining and de-staining, it is expected that in vitro artifacts will be reduced. Finally, MS analyses of RAMA-stained protein bands were revealed not to have been methylated.

Effect of dopant type on the properties of polyaniline

AbstractThe comparative study on the effect of different type of dopants on the properties of polyaniline (PANI) is relative less although dopant has profound effect of the properties of PANI. So, the aim of the present work is to study the effect of different type of dopant, namely strong inorganic hydrochloric acid (HCl), organic and aromatic acids containing different aromatic substitution, namely p‐toluene sulfonic acid (PTSA), dodecylbenzenesulfonic acid (DBSA), organic and aliphatic acids having long hydrocarbon chain, namely lauric acid (LA), on the properties of PANI. The PANI was prepared through oxidative polymerization methods and doped with HCl, PTSA, DBSA, and LA and then characterized through different methods like conductivity measurement, UV, X‐ray, DSC, TGA, and SEM. It was found that the properties of doped PANI depend on the type and molecular size of the dopant. With the increase in dopant chain length, the crystallinity is decreased, whereas the d‐spacing, interchain separation, and solubility are increased. The bond formation of water molecules with the backbone nitrogen of the polymers is much less in presence of aromatic dopants when compared with those of inorganic or aliphatic dopants. All the doped polyanilines under investigation do not decompose up to 500°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009