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4-Bilet, Bioxilma-xillik tadbir, Seminarlar jadvali, 2 5402080461839140018, bir xil maxrajli kasrlarni qoshish va, bir xil maxrajli kasrlarni qoshish va, 3-sinfda massa olchovlarini orgatish metodikasi (1), boshlangich sinf matematikasida miqdor tushunchasini orgatish metodikasi (1), 6-bilet Fuqarolik jamiyati ijtimoiy tuzilmasida mulkdorlar sinfining o‘rni, 1. Teng to’plamlar. To’plam osti. Universal to’plam, Jabborova Iqbol amiyatni boshqarishda fuqarolik jamiyati institutlarining roli, УрГУ - оборудование объявление, Sonlarni yaxlitlash (Aim.uz), Pedagogik texnologiya innovatsiya integratsiya, 1487046332 8-sinf-mehnat-namuna

Chitin and chitosan-derivatives have gained wide attention as effective biosorbents due to low cost and high contents of amino and hydroxyl functional groups which show significant adsorption potential for the removal of various aquatic pollutants. In this review, an extensive list of chitin- and chitosan-derivatives from vast literature has been compiled and their adsorption capacities for various aquatic pollutants as available in the literature are presented. This paper will give an overview of the principal results obtained during the treatment of water and wastewater utilizing chitin and chitosan-derivatives for the removal of: (a) metal cations and metal anions; (b) radionuclides; (c) different classes of dyes; (d) phenol and substituted phenols; (e) different anions and other miscellaneous pollutants. The review provides a summary of recent information obtained using batch studies and deals with the various adsorption mechanisms involved. It is evident from the literature survey that chitin- and chitosan-derivatives have shown good potential for the removal of various aquatic pollutants. However, still there is a need tofind out the practical utility of such developed adsorbents on commercial scale.

Xitin va xitosan hosilalari turli xil suvli ifloslantiruvchi moddalarni olib tashlash uchun muhim adsorbsion potentsialni ko'rsatadigan aminokislotalar va gidroksil funktsional guruhlarning arzonligi va yuqori miqdori tufayli samarali biosorbents sifatida keng e'tibor qozondi. Ushbu sharhda keng adabiyotdan olingan xitin- va xitosan-lotinlarning keng ro'yxati tuzilgan va ularning adabiyotda mavjud bo'lgan turli xil suv ifloslantiruvchi moddalarni adsorbtsiya qilish imkoniyatlari berilgan. Ushbu hujjatda xitin va xitosan hosilalarini ishlatib suv va oqava suvlarni tozalash jarayonida olingan asosiy natijalar haqida qisqacha ma'lumot beriladi: (a) metall kationlari va metall anionlari; (b) radionuklidlar; (v) turli xil bo'yoq sinflari; (d) fenol va uning o'rnini bosuvchi fenollar; (e) turli xil anionlar va boshqa har xil ifloslantiruvchi moddalar. Sharh partiyaviy tadqiqotlar yordamida olingan so'nggi ma'lumotlarning qisqacha mazmunini va turli adsorbsion mexanizmlarni o'rganishni o'z ichiga oladi. Adabiy tadqiqotlar shuni ko'rsatadiki, xitin va xitosan hosilalari turli xil suvli ifloslantiruvchi moddalarni olib tashlash uchun yaxshi imkoniyatlarga ega. Shu bilan birga, tijorat miqyosida bunday rivojlangan adsorbentlarning amaliy foydasini aniqlash zarurati mavjud.



1. Introduction

Water is one of the basic necessities required for the sustenance and continuation of life. It is therefore important that supply of good quality water should be available for various activities. However, this is becoming increasingly difficult in view of large scale pollution caused by industrial, agricultural and domestic activities. These activities generate wastewater which contains both inorganic and organic pollutants. Some of the common pollutants are phenols, dyes, detergents, insecticides, pesticides and heavy metals[1]. The nature of pollutants in wastewater depends on the source of generation and varies from place to place. These pollutants are often toxic and cause adverse affects on human and animal life if present above certain concentration levels. In order to avoid pollution of natural water bodies, it is essential to treat wastewater for the removal of pollutants before being discharged into them. A number of methods such as coagulation, membrane process, adsorption, dialysis, foamflotation, osmosis, photocatalytic degradation and biological methods have generally been used for the removal of toxic pollutants from water and wastewater[2]. The type of the process to be employed may depend on nature of pollutant. However, adsorption process is often considered most appropriate as it can remove both inorganic and organic pollutants and the operation of the process is convenient. Activated carbon has been found to be a universal adsorbent for effluent treatment and is commonly used for the removal of various pollutants from water[3]. However, its widespread use in wastewater treatment is sometimes restricted due to its higher cost. It is now recognized that adsorption using low-cost adsorbents is an effective and economic method for water decontamination. A large variety of nonconventional adsorbents have been examined for their ability to remove various types of pollutants from water and wastewater. Biosorbents gain wide attention as these are available in large quantities worldwide and are eco-friendly. The use of adsorbents containing natural polymers has received reorganization, in particular polysaccharides such as chitin and its derivate chitosan. Chitin wasfirst discovered in mushrooms by the French Professor, Henrni Braconnot, in 1811. In 1820s chitin was also isolated from insects. Chitin contains 2-acetamido-2-deoxy-β-D-glucose through aβ (1→4) linkage. Chitin is the most abundant naturalfiber next to the cellulose and is similar to cellulose in many respects. The most abundant source of chitin is the shell of crab and shrimp. Chitosan was discovered in 1859 by Professor C. Rouget. Chitosan contains 2-acetamido-2-deoxy-β-D-glucopyranose and 2-amino-2-deoxy-β-D-glucopyranose residues. Chitosan has drawn particular attention as effective biosorbent due to its low cost compared to activated carbon and its high contents of amino and hydroxyl functional groups showing high adsorption potential for various aquatic pollutants[4–8]. This biopolymer represents an attractive alternative to other biomaterials because of its physico-chemical characteristics, chemical stability, high reactivity, excellent chelation behavior and high selectivity toward pollutants[4–8]. Natural chitosan has been modified by several methods (either physically or chemically) in order to enhance the adsorption capacity for various types of pollutants. Different shapes of chitosan, e.g. membranes, microspheres, gel beads andfilms have been prepared and examined for the removal of various pollutants from water and wastewater. The detailed description about structures of chitin and chitosan and their physical and chemical modification by various techniques has been documented in detail in earlier reviews[4–10]. Previous review articles discussed the potentialof chitin and chitosan for metal ions[5–7,9]or dyes[8]. However, one of the aims of this review is to compile and present the adsorption potential (adsorption capacities) of chitin- and chitosan-derivatives for various other aquatic pollutants e.g. phenol and substituted phenols; different anions and miscellaneous pollutants such as pesticides, fungicides, humic substances etc. This review provides, besides the critical discussions, the recent literature of about the past 10–15 years to demonstrate the usefulness of chitin- and chitosan-derivatives in water and wastewater applications. A summary of relevant published data (in terms of adsorption capacities of chitin and chitosan-derivatives for the removal of various different pollutants) with some of the latest important findings and giving a source of up-to-date literature on the adsorption properties of chitin and chitosan for diverse types of pollutants is presented and some of the results have been discussed here.

1.Kirish


Suv hayotni ta'minlash va davom ettirish uchun zaruriy narsalardan biridir. Shuning uchun har xil tadbirlar uchun sifatli suv ta'minoti mavjud bo'lishi juda muhimdir. Biroq, bu sanoat, qishloq xo'jaligi va maishiy faoliyat natijasida kelib chiqadigan katta miqdordagi ifloslanish tufayli murakkablashmoqda. Ushbu tadbirlar noorganik va organik ifloslantiruvchi moddalarni o'z ichiga olgan oqava suvlarni hosil qiladi. Umumiy ifloslantiruvchi moddalarning ba'zilari fenollar, bo'yoqlar, yuvish vositalari, insektitsidlar, pestitsidlar va og'ir metallardir [1]. Oqava suvlardagi ifloslantiruvchi moddalarning tabiati hosil bo'lish manbasiga bog'liq va har joyda turlicha bo'ladi. Ushbu ifloslantiruvchi moddalar ko'pincha zaharli bo'lib, ma'lum kontsentratsiyadan yuqori bo'lsa, inson va hayvonlar hayotiga zararli ta'sir ko'rsatadi. Tabiiy suv havzalarining ifloslanishiga yo'l qo'ymaslik uchun ifloslantiruvchi moddalarni uloqtirishdan oldin ularni tozalash uchun oqava suvlarni tozalash kerak. Koagulyatsiya, membrana jarayoni, adsorbsiya, dializ, ko'piklanish, osmos, fotokatalitik buzilish va biologik usullar kabi bir qator usullar asosan suv va oqova suvlardan toksik ifloslantiruvchi moddalarni olib tashlash uchun ishlatilgan [2]. Amalga oshiriladigan jarayonning turi ifloslantiruvchi xususiyatga bog'liq bo'lishi mumkin. Shu bilan birga, adsorbsiya jarayoni ko'pincha eng maqbul deb hisoblanadi, chunki u noorganik va organik ifloslantiruvchi moddalarni olib tashlashi mumkin va bu jarayon qulay. Faollashtirilgan uglerod oqova suvlarni tozalash uchun universal adsorbent ekanligi aniqlandi va odatda turli xil ifloslantiruvchi moddalarni suvdan tozalash uchun ishlatiladi [3]. Biroq, undan oqava suvlarni tozalashda keng foydalanish ba'zan uning narxi yuqori bo'lgani sababli cheklanadi. Endi arzon narxdagi adsorbanlar yordamida adsorbtsiya suvni zararsizlantirish uchun samarali va iqtisodiy usul ekanligi aniqlandi. Noan'anaviy adsorbentlarning turli xil ifloslantiruvchi moddalarni suv va oqava suvlardan tozalash qobiliyati tekshirildi. Biosorbentslar katta e'tiborni jalb qilmoqda, chunki ular dunyoda ko'p miqdorda mavjud va ekologik jihatdan xavfsizdir. Tabiiy polimerlarni o'z ichiga olgan adsorbentlardan foydalanish, ayniqsa chitin va uning hosilasi xitosan kabi polisaxaridlarni qayta tashkil etishni oldi. Chitin qo'ziqorinlardan birinchi marta frantsuz professori Genri Brakonnot tomonidan 1811 yilda kashf etilgan. 1820 yillarda xitin hasharotlardan ham ajralib chiqqan. Xitin a 2 (1 → 4) aloqasi orqali 2-atsetamido-2-deoksidi-β-D-glyukozani o'z ichiga oladi. Chitin tsellyuloza yonidagi eng ko'p uchraydigan tabiiy toldir va ko'p jihatdan tsellyuloza o'xshash. Xitinning eng mo'l manbai - qisqichbaqa va qisqichbaqalar qobig'i. Chitosan 1859 yilda professor C. Ruget tomonidan kashf etilgan. Chitosan tarkibida 2-atsetamido-2-deoksid-β-D-glyukopiranoz va 2-amino-2-deoksid-β-D-glyukopiranoz qoldiqlari mavjud. Chitosan, faol uglerodga nisbatan arzonligi va turli xil suvli ifloslantiruvchi moddalarga yuqori adsorbsion potentsialga ega bo'lgan amino va gidroksil funktsional guruhlarga nisbatan past narxliligi tufayli samarali biosorbent sifatida alohida e'tibor qaratdi [4–8]. Ushbu biopolimer fizik-kimyoviy xususiyatlari, kimyoviy barqarorligi, yuqori reaktivligi, ajoyib chelash xatti-harakati va ifloslantiruvchi moddalarga nisbatan yuqori selektivligi tufayli boshqa biomateriallarga jozibador alternativa bo'lib xizmat qiladi (4–8). Tabiiy xitozan turli xil ifloslantiruvchi moddalarning adsorbsion qobiliyatini oshirish uchun bir necha usul bilan (fizikaviy yoki kimyoviy) o'zgartirildi. Xitosanning turli xil shakllari, masalan. turli xil ifloslantiruvchi moddalarni suv va oqava suvlardan tozalash uchun membranalar, mikrosferalar, jel boncuklar va filflar tayyorlandi va tekshirildi. Xitin va xitosan tuzilmalari va ularning turli xil texnikaviy fizik-kimyoviy modifikatsiyalari to'g'risidagi batafsil ma'lumotlar avvalgi sharhlarda batafsil hujjatlashtirilgan [4–10]. Oldingi sharh maqolalarida xitin va xitosanning metall ionlari uchun potentsiali muhokama qilingan [5–7,9] yoki bo'yoqlar [8]. Shu bilan birga, ushbu sharhning maqsadlaridan biri xitin va xitosan hosilalarining adsorbtsion potentsialini (adsorbtsiya sig'imi) yig'ish va taqdim etish, masalan, boshqa suvli ifloslantiruvchi moddalar uchun. fenol va uning o'rnini bosuvchi fenollar; turli xil anionlar va turli xil ifloslantiruvchi moddalar, masalan, pestitsidlar, qo'ziqorinlar, hümik moddalar va boshqalar. Ushbu sharh tanqidiy munozaralardan tashqari, so'nggi 10-15 yil ichida suv va oqova suvlardagi xitin va xitosan hosilalarining foydali ekanligini namoyish etish bo'yicha so'nggi adabiyotlarni taqdim etadi. ilovalar. Chitinning adsorbsion xossalari bo'yicha eng so'nggi topilmalar bilan bir qatorda nashr etilgan ma'lumotlarning qisqacha mazmuni (turli xil ifloslantiruvchi moddalarni olib tashlash uchun xitin va xitosan hosilalarining adsorbsion imkoniyatlari nuqtai nazaridan). va har xil ifloslantiruvchi moddalar uchun xitosan taqdim etildi va natijalarning bir qismi bu erda muhokama qilindi.

2. Chitin- and chitosan-derivatives for detoxification of water and wastewater 2.1. Chitin- and chitosan-derivatives for metals (cations and anions) and radionuclides removal Metal ions are one of the important categories of water pollutants, which are toxic for humans through the food-chain pyramid. Various toxic heavy metal ions discharged into the environment through different industrial activities, constituting one of the major causes of environmental pollution. Chitin- and chitosan-derivatives have been extensively investigated as adsorbents for the removal of metal ions from water and wastewater. The high adsorption potential of chitosan for heavy metals can be attributed to (1) high hydrophilicity due to large number of hydroxyl groups of glucose units, (2) presence of a large number of functional groups, (3) high chemical reactivity of these groups, and (4)flexible structure of the polymer chain[10]. Cadmium and its compounds are extremely toxic even in low concentrations, and bioaccumulate in organisms and ecosystems. A disease known as“Itai Itai” in Japan is associated with cadmium poisoning, which results in multiple fractures in the body. Chitin has been explored as adsorbent for the removal of cadmium (Cd) ions from aqueous solutions by batch experiments [11]. An adsorption capacity of 14 mg/g of chitin for Cd(II) ions was observed. Scanning electron microscopy coupled with X-ray energy dispersed analysis was used to demonstrate that cadmium-containing nodules existed on the chitin surface for cadmium-equilibrated chitin. They also examined the effect of co-ions (Cu 2+and Zn2+) on the cadmium biosorption at free solution pH and 25 °C, in static conditions[12]. Biosorption of individual metals followed the sequence: Cu>Cd>Zn. Zn 2+ ions had little affect on cadmium uptake capacity of chitin under the conditions examined, whereas, the presence of Cu 2+ ions decreased the affinity of chitin for cadmium. The efficiency of cadmium removal using chitosan has also been investigated by Jha et al. [13]. An adsorption capacity of 5.93 mg of Cd(II)/g of chitosan at a pH range of 4.0–8.3 was reported and the presence of ethylenediaminetetraacetic acid (EDTA) was found to significantly decrease cadmium removal. This is expectable, because EDTA and other aminopolycarboxylic acids are known to form extremely stable complexes with heavy metals[14,15]. Mercury (Hg), copper (Cu), nickel (Ni), zinc (Zn), lead (Pb) and manganese (Mn) are some of the other metals ions, which are of major concern when present at higher concentrations in the environment. Their removal has been investigated from water by several researchers by chitin and chitosan-derivatives. McKay et al. investigated the adsorption of some metal ions by chitosan[16]. It was found that the adsorption capacity of chitosan for Hg(II), Cu(II), Ni(II) and Zn(II) were 815, 222, 164 and 75 mg/g, respectively. The ability of chitin or chitosan to sorb Cu(II) ions from aqueous solutions was studied, taking into account kinetic, equilibrium, and mass transfer aspects [17]. Equilibrium isotherm studies revealed that the Cu(II) sorption onto chitin and chitosan was best described by the Langmuir and RedlichPeterson models. The sorption capacity of chitosan for Cu(II) ions was four tofive times higher than that of chitin. The use of chitosanflakes for the removal of Cu 2+ from water has been examined[18]. Chitosan showed excellent ability for Cu 2+ adsorption with a capacity of 1.8–2.2 mmol/g dry mass. However, the capacity sharply rises when the solutions contain a high concentration of chloride ions. The variation of solution pH leads to competition between the coordination of Cu 2+ with chitosan. The optimal pH range for copper adsorption onto chitosanflakes was 5.4–6.0. The performance of commercially available sources of hitin, chitosan and chitosan cross-linked with benzoquinone for various metal ions has also been explored[19]. Initial pH of the metal solution significantly influenced metal uptake capacity. The highest metal uptake values (137, 108, 58, and 124 mg/g for copper, zinc, arsenic, and chromium, respectively) were achieved with chitosan (1 g/L, at pH 4) with initial metal concentrations of 400 mg/L. Simultaneous removal of various metal ions (zinc, copper, cadmium, and lead) using commercially available chitosan flakes from aqueous solutions under variable physico-chemical conditions has also been reported[20]. The results obtained from the adsorption studies showed that there was significant uptake of these metal ions by chitosan. Chitosanflakes exhibited maximum uptake capacity for copper ions. The order of metal ion adsorption by chitosan decreased from Cu 2+ to Zn 2+ as follows: copper lead>cadmium>zinc. The heavy metal uptake by chitosan was found to be pH dependent. The uptake of metal ions by chitosan was enhanced by increasing the pH from 4 to 7. This was attributed to the greater availability of amino groups at higher pH.

2. Suv va oqava suvlarni zararsizlantirish uchun xitin va xitosan hosilalari 2.1. Metall ionlari (kationlar va anionlar) va radionuklidlarni olib tashlash uchun xitin va xitosan hosilalari Metall ionlari oziq-ovqat zanjiri piramidasi orqali odamlar uchun zaharli bo'lgan suv ifloslantiruvchi moddalarning muhim toifalaridan biridir. Turli xil sanoat faoliyati natijasida atrof-muhitga turli xil toksik og'ir metal ionlari chiqarilishi atrof-muhitning ifloslanishining asosiy sabablaridan biridir. Xitin va xitosan hosilalari metal ionlarini suv va oqava suvlardan tozalash uchun adsorbent sifatida keng miqyosda o'rganilgan. Xitozanning og'ir metallar uchun yuqori adsorbsion potentsialiga (1) glyukoza birliklarining gidroksil guruhlarining ko'pligi, (2) ko'p sonli funktsional guruhlarning mavjudligi, (3) ushbu guruhlarning yuqori kimyoviy reaktivligi tufayli yuqori gidrofilikka bog'liqlik kiradi. , va (4) polimer zanjirning moslashuvchan tuzilishi [10]. Kadmiy va uning birikmalari past konsentratsiyada ham o'ta zaharli hisoblanadi va organizmlar va ekotizimlarda bioakkumulyatsiya qilinadi. Yaponiyada "Itai Itai" nomi bilan ma'lum bo'lgan kasallik kadmiydan zaharlanish bilan bog'liq bo'lib, natijada tanadagi ko'plab yoriqlar paydo bo'ladi. Chitin suvli eritmalardan kadmiy (Cd) ionlarini ommaviy eksperimentlar yordamida olib tashlash uchun adsorbent sifatida o'rganilgan [11]. Cd (II) ionlari uchun 14 mg / g xitinning adsorbsion sig'imi kuzatildi. Skanerlash elektron mikroskopi rentgen nurlari bilan tarqatilgan analiz yordamida kadmiyum muvozanatlangan chitin uchun chitin yuzasida kadmiyum o'z ichiga olgan nodullar mavjudligini namoyish etish uchun ishlatilgan. Shuningdek, ular ko-ionlarning (Cu 2 + va Zn2 +) erkin eritmadagi pH va 25 ° C da statik sharoitda kadmiyning biosorbtsiyasiga ta'sirini o'rganib chiqdilar [12]. Ayrim metallarning biosorbtsiyasi ketma-ketlikda amalga oshirildi: Cu> Cd> Zn. Ko'rib chiqilgan sharoitlarda Zn 2+ ionlari xitinning kadmiyga tushish qobiliyatiga oz ta'sir ko'rsatdi, ammo Cu 2+ ionlarining mavjudligi xitinning kadmiyga yaqinligini kamaytirdi. Xitosan yordamida kadmiyni yo'q qilish samaradorligi, shuningdek, Jha va boshqalar tomonidan o'rganilgan. [13]. PH 4.0-8.3 oralig'ida 5.93 mg Cd (II) / g xitosanning adsorbsion sig'imi qayd etildi va etilendiaminetetraacetic kislotasi (EDTA) mavjudligi kadmiyni yo'q qilishni sezilarli darajada kamaytirdi. Buni kutish mumkin, chunki EDTA va boshqa aminopolokarboksilik kislotalar og'ir metallarga ega bo'lgan o'ta barqaror komplekslarni hosil qiladi [14,15]. Merkuriy (Hg), mis (Cu), nikel (Ni), rux (Zn), qo'rg'oshin (Pb) va marganets (Mn) - bu boshqa metal ionlari bo'lib, ular atrof-muhitda yuqori konsentratsiyada mavjud bo'lganda juda muhimdir. . Ularning suvdan olib tashlanishi bir nechta tadqiqotchilar tomonidan xitin va xitosan-derivativlar tomonidan o'rganilgan. McKay va boshq. Ba'zi metal ionlarining xitosan tomonidan adsorbsiyasini o'rgangan [16]. Xitosanning Hg (II), Cu (II), Ni (II) va Zn (II) uchun adsorbsion kuchi mos ravishda 815, 222, 164 va 75 mg / g ekanligi aniqlandi. Xitin yoki xitosanning suvli eritmalardan Cu (II) ionlarini so'rib olish qobiliyati kinetik, muvozanat va massa uzatish tomonlarini hisobga olgan holda o'rganildi [17]. Muvozanat izotermini o'rganish natijasida Cu (II) ning xitin va xitosanga singishi Langmuir va RedlichPeteron modellari tomonidan eng yaxshi tasvirlanganligi aniqlandi. Cu (II) ionlari uchun xitosanning sorbsion sigiti xitinga nisbatan to'rt baravar yuqori edi. Cu 2+ ni suvdan olib tashlash uchun xitosanflaklardan foydalanish ko'rib chiqilgan [18]. Chitosan Cu 2+ adsorbsiyasi uchun 1,8-2,2 mmol / g quruq massaga ega. Shu bilan birga, eritmalar xlorid ionlarining yuqori konsentratsiyasini o'z ichiga olganda, quvvat keskin ko'tariladi. Eritmaning pH o'zgaruvchanligi Cu 2+ ni xitosan bilan muvofiqlashtirish o'rtasidagi raqobatga olib keladi. Misni xitosanflaklarga adsorbsiyasi uchun optimal pH oralig'i 5.4–6.0. Savdoda mavjud bo'lgan xitin, xitosan va xitosanning turli xil metal ionlari uchun benzokinon bilan o'zaro bog'liqligi o'rganildi [19]. Metall eritmaning dastlabki pH qiymati metalni ushlab turish qobiliyatiga sezilarli ta'sir ko'rsatdi. Xitosan (1 g / L, pH 4) 400 mg dastlabki metal kontsentratsiyasi bilan eng yuqori metalni yutish ko'rsatkichlariga (mis, rux, mishyak va xrom uchun mos ravishda 137, 108, 58 va 124 mg / g) erishildi. / L O'zgaruvchan fizik-kimyoviy sharoitlarda turli xil metall ionlarini (tsink, mis, kadmiy va qo'rg'oshin) suvli eritmalardan xitosan parchalari yordamida bir vaqtning o'zida olib tashlash haqida ham xabar berilgan [20]. Adsorbsiya tadqiqotlaridan olingan natijalar xitosan tomonidan ushbu metal ionlarini sezilarli darajada ushlab turishini ko'rsatdi. Chitosanflakes mis ionlari uchun maksimal quvvatni namoyish qildi. Xitosan tomonidan metal ionlarini adsorbtsiya qilish tartibi Cu 2+ dan Zn 2+ gacha pasaygan: mis qo'rg'oshin> kadmiy va rux. Xitosanning og'ir metalni yutishi pH ga bog'liq ekanligi aniqlandi. Xitosan tomonidan metal ionlarini qabul qilish pH ni 4 dan 7 ga ko'tarish orqali yaxshilandi. Bu aminokislotalarning yuqori pH darajasida bo'lishiga bog'liq.

On the other hand, the reduced adsorption of metal ions at acidic pH values could be attributed to the fact that at 27 A. Bhatnagar, M. Sillanpää / Advances in Colloid and Interface Science 152 (2009) 26–38 Author's personal copy lower pH, the metal ions that would coordinate with the lone pair of nitrogen would have to compete with H3O + for an active site. Several chemical modifications have been carried out to increase the uptake capacity of cross-linked chitosan beads[21].Amongthem, aminated chitosan beads formed by the chemical reaction of ethylenediamine and carbodiimide showed the highest uptake capacity for mercury (Hg2+ ions. The uptake capacity of aminated chitosan beads was ca. 2.26 mmol Hg 2+ /g dry mass at pH 7. This value was thought to be one of the highest uptake capacities among various biosorbents. Beads also showed the characteristic of competitive sorption between mercury and hydrogen ions and finally it was successfully modelled by an equilibrium model based on isothermal sorption data. Recently, Hg(II) removal from water by chitosan and its derivatives has extensively been reviewed by Miretzky and Cirelli [9]. To enhance the sorption capacity of chitosan for Cd removal, Rorrer et al. performed experiments to increase the porosity of the chitosan beads by adding acidic chitosan solution into a sodium hydroxide solution precipitation bath[22]. The gelled chitosan beads were cross-linked with glutaraldehyde and then freeze dried. Beads of 1- and 3-mm diameter were prepared. Beads of 1-mm diameter possessed surface areas exceeding 150 m2/g and mean pore sizes of 560 Å and were insoluble in acid media at pH 2.Adsorption isotherms at 25 °C and pH 6.5 over the concentration range 1–1690 mg Cd 2+ /L possessed a stepped shape and maximum adsorption capacities for the 1- and 3-mm beads were found to be 518 and 188 mg of Cd/g of beads, respectively. The stepped shape of the isotherm was explained by a pore-blockage mechanism. The modified chitosan showed many advantages overflaked or powdered chitosan e.g. higher internal surface area, and cross-linkage of beads making them insoluble in low-pH solutions, thus proving their suitability over a broad pH range. A new composite chitosan biosorbent was prepared by coating chitosan on to perlite ore and investigated for Cu(II) and Ni(II) removal [23]. Maximum removal of Cu(II) and Ni(II) on chitosan coated on perlite was at pH 5.0. The maximum monolayer adsorption capacity of chitosan coated on perlite was 196.07 mg/g for Cu(II) and 114.94 mg/g for Ni(II). Chitosan obtained from silkworm chrysalides (ChSC) was examined for the removal of Pb 2+ and Cu2+ from battery manufacture wastewater[24]. The best pure ChSC deacetylation degrees (DDs) obtained for the removal of Pb2+and Cu 2+ from battery wastewater were 80% (90 min ChSC deacetylation) and 92% (180 min ChSC deacetylation), respectively. The maximum adsorption capacities for Pb 2+and Cu2+ using pure ChSC with 80% and 92% DD were 72 mg/g and 87 mg/g, respectively, under the experimental conditions: pH 5.0, particle size from 300 to 425 µm, temperature 20.0 ±0.1 °C, and 250 rpm stirring. Three cross-linked chitosan-derivatives were used as sorbents for the removal of Cu(II) from aqueous solutions[25]:(i)Ch, without grafting; (ii)Ch-g-Aam, grafted with acrylamide; and (iii) Ch-g-Aa,graftedwith acrylic acid.Ch-g-Aamaterial presented the highest sorption capacity for Cu(II) removal (318 mg/g at pH 6) among the studied and earlier cited chitosan materials. The interaction between Cu(II) and the prepared sorbents was confirmed by FTIR spectroscopy. The peaks of amino groups of Cu(II)-loaded chitosan sorbents presented shifts with respect to non-loaded ones (Ch,1665–1660 cm −1 ; Ch-g-Aam,1672–1674 cm−1;Ch-g-Aa,1674–1670 cm−1), suggesting a chelated complex. New chitosan-derivative has been synthesized by cross-linking a metal complexing agent, [6,6′-piperazine-1,4-diyldimethylenebis (4-methyl-2-formyl) phenol] (L), with chitosan (CTS) by Krishnapriya and Kandaswamy[26]. Adsorption experiments (pH dependency, kinetics, and equilibrium) of the cross-linked chitosan ligand (CCTSL) of various metal ions such as Mn(II), Fe(II), Co(II), Cu(II), Ni(II), Cd(II) and Pb(II) were carried out at 25 °C. The results showed that the adsorption was dependent on pH of the solution, with maximum capacity between pH 6.5 and 8.5. The order of adsorption capacities for the metal ions studied was found to be Cu(II) > Ni(II) > Cd(II)≥Co(II)≥Mn(II)≥Fe(II)≥Pb(II). Chemical sorption was suggested as the rate-limiting step of adsorption mechanism. A new biosorbent was developed by coating chitosan on to polyvinyl chloride (PVC) beads[27]. Equilibrium and column flow adsorption characteristics of copper(II) and nickel(II) ions on the biosorbent were studied. The maximum monolayer adsorption capacity of chitosan-coated PVC sorbent as obtained from Langmuir adsorption isotherm was found to be 87.9 mg/g for Cu(II) and 120.5 mg/g for Ni(II) ions, respectively.

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