pH Value Of Reaction System Research Articles

Sonochemical synthesis of battery-type ZnCo2O4 electrode material with huge specific surface area for advanced hybrid supercapacitors

Sonochemistry is a novel and efficient method for the synthesis of electrode materials within micro-/nano-scale. In this work, the ZnCo2O4 nanoparticles (NPs) and chain-like ZnCo2O4 nanostructures, namely ZnCo2O4–7.5 and ZnCo2O4–9.5, were sonochemically prepared by controlling the pH value of reaction system combined with an extra calcination. The ZnCo2O4–7.5 NPs exhibited a larger specific surface area (SSA) of 148.77 m2 g−1, and presented better electrochemical properties such as a high specific capacity (Cs) of 331.2C g−1 under 2 A g−1 along with 82.5 % rate performance at 10 A g−1. As for the ZnCo2O4–9.5 nanostructure, it delivered an inferior Cs of 274.8C g−1 and showed a moderate rate capability with 75.6 % capacity retention, accordingly. The hybrid supercapacitor (HSC) device was assembled using such ZnCo2O4–7.5 NPs (ZnCo2O4–9.5 nanostructure) as cathode and activated carbon (AC) as anode to explore the application potential in the field of electrochemical energy storage. After 7000 cycles at the current density of 8 A g−1, both ZnCo2O4–7.5//AC and ZnCo2O4–9.5//AC HSCs showed outstanding cyclic stabilities with 100.4 % and 105.1 % of initial capacity retention, respectively. Meanwhile, the ZnCo2O4–7.5//AC HSC delivered a high energy density (Ed) of 38.1 W h kg−1 at the power density (Pd) of 1002.0 W kg−1, and it could still hold 26.3 W h kg−1 at the higher Pd of 9136.5 W kg−1. In contrast, the ZnCo2O4–9.5//AC HSC presented a slightly inferior Ed of 36.8 W h kg−1 at 1104.7 W kg−1. The both types of ZnCo2O4–7.5 and ZnCo2O4–9.5 electrode materials demonstrate excellent electrochemical property, and they can be expected to show brilliant application potential in the field of electrochemical energy storage & conversion when served as electrode materials for high-performance hybrid supercapacitors.

Synthesis and characterization of microencapsulated phase change materials with chitosan-based polyurethane shell

In this paper, chitosan-based polyurethane (c-PU) microencapsulated phase change materials (MicroPCMs) were prepared via the interfacial polymerization reaction of hexamethylene diisocyanate and chitosan accompanied by the charge attraction-assisted. The utilization of natural non-toxic chitosan in MicroPCMs expanded the application of chitosan and guided a new approach to preparing green shell. And the morphology of MicroPCMs with different reaction ration, surfactant and the pH value of reaction system were systematically investigated. The MicroPCMs with c-PU shell exhibited outstanding latent thermal performance (ΔHm = 106.3 J/g, ΔHc = −105.1 J/g), high energy storage efficiency (E = 71.4%), excellent thermal stability and cyclic durability. The c-PU MicroPCMs with reversible photochromic show promising application in the fields of anti-counterfeiting technology and flexible wearable UV protective clothing.

Enhancing H2 evolution and molecular oxygen activation via dye sensitized BiOBr0.9I0.1 under visible light

Sensitization with a dye has great potential for dealing with the photoexcited charge recombination problem for photocatalysts. One of the main factors affecting the dye-sensitization performance is the absorption capacity of semiconductor for dye. Specific surface area of semiconductors and pH values of reaction system are critical for the absorption capacity. Herein, we firstly developed a BiOBr0.9I0.1 solid solution via a facile and fast sacrificial template method. The prepared BiOBr0.9I0.1 has distinct advantages, e.g. loose and rich porous structure, more oxygen vacancies (OVs), and a large specific surface area, which result in strong adsorption for dye molecules. Sensitized by Rhodamine B (RhB), the prepared BiOBr0.9I0.1 photocatalyst shows remarkably improved high activity for H2 evolution, which is 27.9 times than that of the dense structured BiOBr0.9I0.1 under a direct photocatalytic process. By lowing the pH of RhB solution, the absorption ability is further improved because of the protonation of dye. At low pH, the prepared BiOBr0.9I0.1 can efficiently activate the molecular oxygen to produce superoxide radicals (O2−), resulting a super high dye-sensitized degradation activity for tetracycline hydrochloride (TCH) and methyl orange (MO) pollutants, outperforming most catalysts reported under similar conditions by the direct photocatalytic reaction. The present method represents a new direction in the development of dye-sensitization nanomaterials with good performance for energy and environment applications.

Co/C broad band electromagnetic wave absorption composite derived from preferred precursor ZIF-67: preparation and performance

A simple sacrificial template method was used to prepare Co/C composite with cobalt nanoparticles embedded in nitrogen-doped polyporous graphite carbon as an efficient electromagnetic wave (EMW) absorbent. Effects of solvent polarity, ratio of Co2+ to 2-methylimidazole and pH value of reaction system on precursor metal–organic skeleton ZIF-67 were systematically studied by a single variable method, and then the optimal preparation process was obtained. Thermal decomposition time and temperature of precursor ZIF-67 are the keys to the formations of ferromagnetic metal cobalt particles and carbon matrix. Therefore, effects of calcined temperature in inert atmosphere on the carbon content, graphitization degree, magnetic properties and microwave-absorbing performances of Co/C composite prepared were studied, and then nitrogen-doped porous composite Co/C composed of a highly dispersed core–shell Co@graphite nanoparticles coated by amorphous carbon skeleton was successfully prepared by optimizing pyrolysis technology. Composite Co/C-900 obtained by ZIF-67 calcinated at 900 °C exhibits excellent EMW absorption performances at low filling amount; its maximum reflective loss (RLmax) reaches − 34.41 dB at 17.49 GHz with the test thickness of 2.0 mm only, and most importantly, when the test thickness is 2.5 mm, its effective absorption bandwidth (RL < − 10 dB) reaches 7.37 GHz (10.18–17.5 GHz), spanning the X and Ku bands. The synergistic effects of the self-loss (dielectric loss and magnetic dissipation) and structural attenuation (multiple scattering and interface polarization) of Co/C-900 obtained greatly improve its impedance matching with free space and attenuation coefficients to EMW, significantly widening its effective bandwidth. As a new high-performance EMW absorbent with thin thickness, light weight, strong absorption capacity and wide bandwidth, the Co/C composite optimized by precursor preparation and calcination process should have a broad application prospect.

Crystal structures, selective fluorescent sensing and photocatalytic properties of cobalt(II) and copper(II) coordination architectures with 2,4,5-tri(4-pyridyl)-imidazole

Solvothermal reaction of MII (M = Co, Cu) ions with 2,4,5-tri(4-pyridyl)-imidazole (Htpim) gave two MOFs, [Co1.5(tpim)(FA)2(H2O)]n (1) and [Cu2(Htpim)(tpim)(FA)(NO3)2(DMF)]n (2) (HFA = formic acid, DMF = N,N-dimethylformamide). Single-crystal X-ray diffraction analyses indicated that 1 exhibits a 3D {43.412} topology framework assembled by hexanuclear [Co6(FA)8(H2O)4] units and tpim ligands, while 2 presents a 2-D double layer {4.62}2{42.64.82.102}{62.8} network. Hereinto, an inorganic acid was not only used to adjust the pH value of reaction system but also to act as an oxidizing agent to participate in in situ organic reactions. Moreover, 1 displays high sensitivity in the detection of nitrobenzene as a fluorescent sensor and exhibits a relatively good photocatalytic activity toward the degradation of rhodamine B in aqueous solution under UV irradiation.

A Robust, Resilient, and Multi-Functional Soy Protein-Based Hydrogel

Soy protein is one of the most abundant plant protein in nature. Despite numerous studies on soy protein-based materials, the applications of soy protein hydrogel are still extremely limited because of its cumbersome gelation process and poor mechanical properties. Herein, we present a facile method to prepare robust soy protein hydrogels by the introduction of oxidized dextran, a natural polysaccharide derivative, as a macromolecular cross-linking agent. The preparation conditions such as pH value of reaction system and the mass ratio of soy protein to oxidized dextran have been extensively investigated. The resultant soy protein hydrogels exhibit better mechanical properties than the previously reported soy protein-based hydrogels. The best formulated hydrogel shows the compressive modulus of 4.3 kPa and fracture stress of 401 kPa at 87% compression. Also, the hydrogels demonstrate an excellent flexibility to withstand high compression with minimal hysteresis. Owing to the protein and polysaccharides nature of soy protein and dextran, the soy protein hydrogels maintain a good biocompatibility along with excellent mechanical properties. Finally, we show the possibility to design such a soy protein hydrogel as a tolerant multifunctional platform for fluorescence imaging, photothermal therapy, drug carrier, and antibacterial agent. The developed soy protein-based hydrogel is natural, sustainable, robust, and biocompatible and hence has great potential as a multifunctional material for various applications.

Silicon quantum dots with tunable emission synthesized via one-step hydrothermal method and their application in alkaline phosphatase detection

Alkaline phosphatase (ALP) plays an important role in normal growth. Many diseases will occur if the content of ALP is abnormal. Hence, the development of convenient and sensitive assay for monitoring ALP is extremely important. In this work, hydrophilic silicon quantum dots (SiQDs) with tunable emission were synthesized via hydrothermal method. The fluorescent emission of SiQDs was changed easily by adjusting the pH value of reaction system. The detection of ALP activity has been developed by measuring the fluorescence quenching of SiQDs. Quantitative limited evaluation of ALP activity was 1 U/L and the linear relationship was 1 U/L to 7500 U/L. Meanwhile, the fluorescent of as-prepared SiQDs were stable in physiological environment and embodied an excellent anti-interference of ions. High sensitivity and wider detection range, the proposed assay is capable of proved that they could serve as a new species of fluorescence probes for biosensors.

Enzymatic Production of Glutathione Coupling with an ATP Regeneration System Based on Polyphosphate Kinase.

Glutathione (GSH) is an important reducing agent in the living cells. It is synthesized by a two-step reaction and requires two molecules of adenosine triphosphate (ATP) for one molecule GSH. The enzymatic cascade reaction in vitro is a promising approach to achieve a high titer and limit side reactions; although, a cost-effective phosphate donor for ATP regeneration is required. Triphosphate (PolyP(3)), tetraphosphate (PolyP(4)), and hexametaphosphate (PolyP(6)) were investigated in this study. Triphosphate inhibited the bifunctional GSH synthetase (GshF) from Streptococcus agalactiae, while no significant inhibition was observed by adding hexametaphosphate. The polyphosphate kinase from Corynebacterium glutamicum was hence investigated to use hexametaphosphate for regeneration of ATP. Further, the orthogonal experiment, which includes seven factors (buffer concentration, pH value, ADP concentration, GshF dosage, polyphosphate kinase (PPK) dosage, reaction temperature, substrate ratio of amino acid, and reaction times), indicated that the capacity of buffer is the most significant factor of the reaction conditions for enzymatic production of glutathione coupling with a PPK-based ATP regeneration system. After optimizing the Mg2+ concentration, the reaction was scaled up to 250mL in a stirred reactor with pH feedback control to stabilize the pH value of reaction system and nitrogen protection to avoid the oxidation of product. A yield of 12.32g/L was achieved. This work provided a potential GshF-based enzymatic way coupling the PPK-based ATP regeneration to product GSH in the optimal conditions towards cost-effectiveness at the industrial scale.

Ionic liquid-employed synthesis of Bi2E3 (E = S, Se, and Te) hierarchitectures: The case of Bi2S3 with superior visible-light-driven Cr(VI) photoreduction capacity

A general ionic-assisted microwave-ultrasonic combined synthetic strategy was developed to fabricate Bi2E3 (E=S, Se, and Te) hierarchitectures. To understand the crystal phase transformation and morphological evolution of Bi2S3 hierarchical nanostructures, the fabrication of Bi2S3 hierarchitectures was investigated by varying sulfidation time and chlorination time. A topotactic transformation from BiOCl microsphere to Bi2S3 hierarchitectures was proposed. It was found that the structure, size, and morphology of Bi2S3 hierarchitectures could be delicately engineered by varying chlorination time, alkyl chain length, and concentration of ionic liquid. Moreover, the as-prepared Bi2S3 hierarchitectures displayed superior capacity of Cr(VI) photoreduction to P25 and irregular Bi2S3 nanostructures under visible light irradiation. Effects of morphology, pH value of reaction system, Cr(VI) concentration, and catalyst dosage on the Cr(VI) photoreduction capacity of Bi2S3 hierarchitectures were also discussed. The enhancement of photoreduction capacity is not only attributed to the intrinsic good electron transfer ability of Bi2S3, but also to synergetic effects of special architectures, wide photoresponse range, high light photoadsorption, high BET surface area and good electron-hole separation performance. The systematic condition experiments and Cr(VI) photoreduction in electroplating and tannery wastewater experiments further demonstrated that the hierarchical Bi2S3 nanospheres can be used in the actual Cr(VI)-containing wastewater treatment.

Structural Modulation of Nitrate Group with Cations to Affect SHG Responses in RE(OH)2NO3 (RE = La, Y, and Gd): New Polar Materials with Large NLO Effect after Adjusting pH Values of Reaction Systems

A series of rare-earth hydroxide nitrate crystals (La(OH)2NO3, Y(OH)2NO3, and Gd(OH)2NO3) have been synthesized through adjusting pH values of reaction systems under the subcritical hydrothermal condition. All the titled compounds were isostructural with the noncentrosymmetric space group P21 (No. 4) with layer structure, containing [REO9] (RE = La,Y, and Gd) polyhedra in each layer. The polyhedra were stacked on top of each other and further connected with zigzag strings of edge sharing to form infinite corrugated sheets that parallel to the a–c plane. The [NO3] groups that presented two different orientation (A and B) project into the space between the layers. In this study, the angle θ between two different orientation [NO3] groups was defined. With the decrease of ionic radii from La3+, Gd3+ to Y3+, the θ was increased, which led to different second harmonic generation (SHG) effects on lanthanide hydroxide nitrates. The powder SHG measurements revealed that La(OH)2NO3, Gd(OH)2NO3, and Y(OH)2NO3 were p...

Syntheses and topological structures of four luminescent lanthanide phosphonates based on 2-(pyridyl-N-oxide)methylphosphonic acid and oxalic acid

To investigate the synthesis and structure of pyridyl-N-oxide phosphonate ligand based lanthanide complexes, a series of four complexes, namely, [NaLn2(pmpa)(C2O4)2.5(H2O)4]·2H2O {Ln=Sm (1), Eu (2), Gd (3), and Tb (4); H2pmpa=2-(pyridyl-N-oxide)methylphosphonic acid; H2C2O4 =oxalic acid}, were hydrothermally synthesized and characterized by elemental analyses, FT-IR, powder and single-crystal X ray diffraction analyses, and thermogravimetric analyses. In the preparation of complexes 1–4, the pH value of reaction system exhibited a significant impact on the product structures. Complexes 1–4, which are isomorphic, exhibited Na ions involving a three-dimensional 4-nodal topological framework with the point symbol of {42·52·62·73·8}{42·5}{43·5·62}{43·5·63·73}. This framework can be further simplified to a 2-nodal topology with the point symbol of {318·436·533·64}{33}2. Photoluminescence studies of complexes 1, 2 and 4 exhibited characteristic luminescence of Sm(III), Eu(III), and Tb(III) ions, while complex 3 exhibited a Gd(III) ions disturbed ligand emissions.

Facile crystal-structure-controlled synthesis of iron oxides for adsorbents and anode materials of lithium batteries

Iron oxides exhibit excellent physicochemical properties as functional materials because of the diversity of crystal structure. Nano-sized iron oxides, including akaganite (β-FeOOH), maghemite (γ-Fe2O3), ferrihydrite (Fe5HO8∙4H2O) and hematite (α-Fe2O3), were prepared by a facile reflux treatment of iron powder in NaClO solution at 50 °C for 12 h. The crystal structures were controlled by adjusting the pH values of reaction systems. Akaganite, maghemite, ferrihydrite, and hematite were formed when pHs were adjusted to 2–4, 6, 8, and 10, respectively. They showed excellent adsorption performance for As(III), and the adsorption capacity was affected by crystal structure as well as specific surface area. The maximum adsorption capacity for akaganite, maghemite, ferrihydrite, and hematite reached 89.8, 79.1, 78.4, and 63.4 mg g−1, respectively. Hematite showed lithium storage capacity of 2043 mAh g−1 for the first cycle and then kept stable after twenty cycles at a current density of 100 mA g−1. The discharge specific capacity stabilized at 639 mAh g−1 after 100 cycles. The as-prepared iron oxides might be applied as potential adsorbents and anode materials for rechargeable lithium-ion battery.

PVP-assisted synthesis of raspberry-like composite particles

Composite particles composed of SiO2 nanoparticles and polystyrene (PS) spheres with a raspberry-like structure were successfully synthesized by a PVP-assistant sol–gel method. The as-prepared products were systemically characterized by FT-IR, TGA, SEM and TEM. The characterization results indicated that the amount of polyvinyl pyrrolidone (PVP) and concentration of ammonia solution played key roles in tailoring the structure of the composite particles, including size and surface density of SiO2 nanoparticles on the surface of PS spheres. During the PVP-assisted sol–gel process, the synthesized nano-sized SiO2 particles were favorably deposited on the surface of PS spheres to form hierarchical composite particles. By adjusting the amount of PVP and pH value of reaction system, the typical raspberry-like particles with controllable coverage of SiO2 nanoparticles on PS spheres were obtained. Subsequently, the composite particles with well controllable morphology were modified with OcTMS and orderly deposited on the substrate. The effect of the composite particles with different morphologies on the wetting property was investigated. Finally, superhydrophobic surface was generated and the water contact angle was up to 154°. PS–SiO2 composite particles with hierarchical structure were successfully prepared by a PVP-assisted sol–gel method, which exhibited a superhydrophobic property after surface modification with OcTMS.

Modulated preparation and structural diversification of metal–organic frameworks based on 4,4′,4″-(1H-imidazole-2,4,5-triyl)tripyridine ligand

Four metal–organic frameworks with 4,4′,4″-(1H-imidazole-2,4,5-triyl)tripyridine (Htpim), namely {[Cu4(tpim)4](DMAC)(H2O)3}∞ (1), {[Cu(H2tpim)2(H2O)2](NO3)4(H2O)2}∞ (2), {[Zn(Htpim)2(H2O)2](NO3)2(H2O)5}∞ (3) and {[Zn(Htpim)(NO3)(H2O)](NO3)}∞ (4) (DMAC=N,N-dimethylacetamide), have been prepared under solvothermal conditions. Single crystal X-ray diffraction analysis indicates that the ligand Htpim adopts ionized form in 1, protonated form in 2, and primary form both in 3 and 4, respectively, with three types of binding modes including μ2-Npy,Npy mode in 2 and 3, μ3-Npy,Npy,Nim mode in 1 and μ3-Npy,Npy,Npy mode in 4. Different network structures, a 2D 3,4-connected {4.62}2{42.62.82} network of 1, a 1D linear chain of 2 and 3, and a 2D 63 framework of 4, were observed and attributed to different synthetic conditions or metal ions. Nitric acid was used not only to adjust the pH value of reaction system, but also to act as a coordination component in 2–4. Furthermore, luminescent properties have also been studied for these four complexes.

Enhanced Nanohydroxyapatite Formation Using a Hydrolyzed Gelatin

Hydroxyapatite (HAP) nanoparticles were synthesized at room temperature using hydrolyzed gelatin (HG) as an additive. The crystallinity of HAP particles can be effectively controlled by adjusting the concentration of HG additive and the pH value of reaction system. The synthesized product was analyzed by Fourier transform infrared (FTIR) spectrometer, energy dispersive spectrometer (EDS), X‐ray diffractometry (XRD), and transmission electron microscope (TEM). Meanwhile, it was proved that, with HG additive, HAP can be prepared with the calcium‐phosphorus ratio of not only 1.67 but also 1.50. Conventionally, HAP particles need to be synthesized at high temperature with iCa/P = 1.67. Therefore, we believe that this study provides a novel strategy for the preparation of nano‐HAP.

Influence of the pH Value on the Water-Reducing Performance of Polycarboxylate-Based Superplasticizers at Room Temperature

In order to study the effect of the pH value of reaction system on the properties of polycarboxylate-based superplasticizers (PC) and on the cement workability, the PC are synthesized in different pH environments from 3 to 11 at room temperature. The results show the water-reducing performance of PC can be tuned by controlling the pH value of reaction system at room temperature, which affects not only the efficiency and rate of redox initiator systems but also the reactivity of active monomers.

PH-Controlled Two New Co(II) Coordination Polymers Based on 5-Pyrimidyl Benzoic Acid: Synthesis, Structures, and Properties

Two new Co(II) coordination polymers, namely [Co(L)2(H2O)2]n (1) and [Co(HL)(H2O)4]n (2) (HL = 4-pyrimidyl-benzoic acid), have been successfully synthesized through tuning the pH value of reaction system. Single crystal X-ray analysis reveals that compound 1 is a two-dimensional (2D) layer framework, and compound 2 is a zero-dimensional (0D) independent structure. These two compounds are all extended into three-dimensional (3D) supramolecular framework through intramolecular hydrogen bonds. In addition, thermal analysis of these two compounds was also ed.

Monoclinic BiVO4 micro-/nanostructures: Microwave and ultrasonic wave combined synthesis and their visible-light photocatalytic activities

Monoclinic bismuth vanadate (m-BiVO4) micro-/nanostructures with different sizes and morphologies were successfully prepared via a facile and rapid microwave and ultrasonic wave combined technique. The obtained BiVO4 products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and UV–vis diffuse reflection spectroscopy (DRS). It was found that the solvent and pH value had a significant influence on morphology, size and crystalline structure of the product. Nut-like, potato-like and broccoli-like monoclinic BiVO4 were fabricated in different solvents. The crystal phase could be modulated by varying the pH value of reaction system. The photocatalytic activities of the products were also evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation. The result revealed that the photocatalytic activities of BiVO4 nanostructures were closely related to the crystalline phase, band gap and particle size. Monoclinic BiVO4 nanoparticles with small crystal size and large band gap exhibited remarkable photocatalytic performance.

Hydrothermal Synthesis and Characterization of LiZr2(PO4)3

Lithium dizirconium phosphate (LiZr2(PO4)3) possesses good ionic conductivity owing to its unique framework structure and can be used as favorable anode material in Li-ion battery. LiZr2(PO4)3 is commonly prepared by solid phase reaction in which higher temperature is needed and pure LiZr2(PO4)3 without other phases is difficult to obtain in the final products. In this paper, low cost hydrothermal synthesis of pure (LiZr2(PO4)3) was studied. Effects of the hydrothermal conditions (molar ratios of Li+ to ZrOCl2, addition of HF, pH values of reaction system and hydrothermal temperatures) on the phase composition of the products were investigated. The results showed that pure LiZr2(PO4)3 was successfully prepared at lower temperature of 80°C for 24h with the addition of HF when the pH value was adjusted to 5.0 and the molar ratio of Li+ to ZrOCl2 was 0.5 with the concentration of ZrOCl2 as 0.6mol/L. The phases and purity of the final products were characterized by XRD analysis.

Flocculation Kinetics of TiO2-enzyme Microfloccules

TiO2-enzyme microfloccules were prepared by using titanium dioxide nanoparticles as immobilizing carriers, three kinds of polyacrylamide (nonionic, cationic and anionic polyacrylamide) as flocculants and papain as a model of en- zyme. The effects of pH values, dosage and types of polyacrylamide (PAM) on the flocculation and sedimentation behaviour of TiO2-enzyme microfloccules were investigated. The SEM, EDS and particle size analyzer were used to characterize the morphology of TiO2-enzyme microfloccules. The results showed that an effective flocculation was formed among TiO2, pa- pain and different types of PAM flocculant by hydrogen bonding interactions, electrostatic attractions, adsorption bridging action, etc. It was noted that the settling rate of TiO2-enzyme microfloccules, turbidity of the supernatant, floc size and com- pactness of resulting floccules were highly dependent on the PAM dosage. For three kinds of PAM, similar trends of floccu- lation kinetics were observed, a general increase in settling rates were relevant to decrease in turbidity. Attributed to high settling rates, strong flocculation with big size and stable floc occurred with the function of optimum PAM concentrations. But the optimum dosages were different. When the concentration was in the range of 75 mgL -1 to 175 mgL -1 , nonionic PAM (nPAM) displayed the best flocculant performance in all kinds of PAM with a rapid settling rate and large floc size. Moreover, under excessive dosage condition, breakup of floc then occurred. Flocculation kinetics of TiO2-enzyme micro- floccules also could be effectively controlled by changing the pH value of reaction system. Compared nPAM with cationic PAM (cPAM), the microfloccules by using nPAM displayed a high stability and compactness in a wide range of pH values. The settling rate and floc size by using cPAM showed a strong dependence on pH values. It indicated that the immobilized enzyme size could be regulated by the PAM dosage and pH value according to the enzyme structure and properties. Such porous and flexible microstructure was expected to provide the free space as much as possible for the access of substrate molecules to enzyme. Keywords flocculation kinetics; settling rate; particle size distribution; nano TiO2; morphology