Uniform orange-like Fe 3 O 4 /polypyrrole (PPy) composite microspheres have been synthesized using Fe 3 O 4 microspheres as a chemical template under sonication. In the orange-like Fe 3 O 4 /PPy composite microspheres, the Fe 3 O 4 particles played the role of ''seeds'' while the PPy was the ''pulp and peel''. A growth mechanism for the orange-like Fe 3 O 4 /PPy composite microspheres was proposed in which partial pyrrole monomers are immersed into the gaps of Fe 3 O 4 microspheres under sonication, meanwhile Fe 3+ ions released from Fe 3 O 4 microspheres in an acidic environment initiated the polymerization of pyrrole monomers in the interior or around the Fe 3 O 4 microspheres, finally forming an orange-like structure. When used as an absorbent of Cr(VI) ions, the as-obtained Fe 3 O 4 /PPy microspheres showed strong adsorption capability with an adsorption capacity of about 209.2 mg g À1 , which is mainly attributed to the PPy ''pulp and peel''. Furthermore, the magnetic Fe 3 O 4 ''seeds'' in composite microspheres make them easy to separate from wastewater by magnetic separation. Recently, polymers, including polyaniline, polyacrylonitrile, poly(p-phenylenediamine), polypyrrole, and sulfophenylenediamine copolymer, were found to be highly efficient absorbents due to their rich functional groups such as -C]O, -CN, -OH, -COO À , etc. [18][19][20][21][22][23][24][25] These polymers exhibited good adsorption performance for heavy metal ions such as Cr(VI) ions. However, it is difficult to synthesize magnetic-based polymer composite materials, since polymers such as polypyrrole or polyaniline are hydrophobic but the surfaces of magnetic particles are

Well-dispersed magnetic-based silver composite microspheres (Fe 3 O 4 @SiO 2 @Ag) with a nanosheetassembled shell structure were synthesized at room temperature, where sonicating and mechanical stirring techniques were both employed and played important roles during the silver shell growth process. The results show that the nanosheet-assembled silver shell could be obtained and controlled by adjusting the concentration of citrate ions as a morphology directing-reagent. The gaps in or between cross-linked nanosheets in the shell of the composite microspheres were proposed to provide sufficient "hot spots" when they were used as a SERS substrate. The SERS measurements exhibit clear enhancement signals by using R6G as a probe molecule, and even at concentrations as low as 10 À14 M, all enhancement peaks could be observed clearly. The film assembled from the composite microspheres exhibited good reproducibility across the entire area. Additionally, the magnetic Fe 3 O 4 @SiO 2 @Ag microspheres can be separated from solution rapidly, which shortened the detection time. Considering their excellent SERS performance, this kind of composite microsphere, which has both a SERS active shell and a magnetically separable core, would be very useful as an effective SERS substrate for detecting organic pollutants in solution.

To realize highly sensitive and reproducible SERS performance, a new route was put forward to construct uniform SERS film by using magnetic composite microspheres. In the experiment, monodisperse Fe3O4@SiO2@Ag microspheres with hierarchical surface were developed and used as building block of SERS substrate, which not only realized fast capturing analyte through dispersion and collection under external magnet but also could be built into uniform film through magnetically induced self-assembly. By using R6G as probe molecule, the as-obtained uniform film exhibited great improvement on SERS performance in both sensitivity and reproducibility when compared with nonuniform film, demonstrating the perfect integration of high sensitivity of hierarchal noble metal microspheres and high reproducibility of ordered microspheres array. Furthermore, the as-obtained product was used to detect pesticide thiram and also exhibited excellent SERS performance for trace detection.

Highly water-dispersible and monodispersed Fe 3 O 4 hollow microspheres have been synthesized by a simple one-pot hydrothermal method, in which sodium polyacrylate (PAAS) was used as a dispersant and size-controlling reagent. The results showed that the obtained Fe 3 O 4 hollow microspheres were composed of nanoparticles less than 15 nm in diameter and exhibited superparamagnetic properties with relatively high saturation magnetization at room temperature. Meanwhile, the negatively-charged carboxyl groups from PAAS were closely attached to the surface of the Fe 3 O 4 hollow microspheres, which made them highly water-dispersible. The reaction process was systematically investigated and we found that the Fe 3 O 4 hollow microspheres in our experiment were formed through a self-template process, where the solid a-Fe 2 O 3 microspheres generated at the initial stage transformed into Fe 3 O 4 hollow microspheres through the synergetic effect of Ostwald ripening and reduction. Additionally, the PAAS, by regulating the viscosity of the reaction solution through varying the concentration, could indirectly adjust the size of the Fe 3 O 4 hollow microspheres ranging from 200 nm to 340 nm. Finally, the obtained Fe 3 O 4 hollow microspheres were demonstrated to be an excellent adsorbent of heavy metal ions like Pb 2+ due to their abundant carboxyl groups and magnetic separability.

Hierachical FeO microspheres with superparamagnetic properties are attractive for their superior structural, water-dispersible, and magnetic separation merits. Here self-template etching route was developed to create optimal porous structure in superparamagnetic FeO microspheres by using the oxalic acid (HCO) as etching agent. A plausible formation mechanism of the urchin-like FeO microspheres was proposed based on systematic investigation of the etching process, which involved two stages including pore-forming step based on size-selective etching and pore-expanding step based on further etching. The as-synthesized FeO microspheres exhibited urchin-like structure with specific surface area and pore-size tunable, water-dispersible, and superparamagnetic properties. The optimal urchin-like FeO microspheres demonstrated superior performance including fast magnetic separation and high removal capabilities for the heavy metals ions like Pb (112.8 mg g) and Cr(VI) (68.7 mg g). This work will shed new light on the synthesis of urchin-like microspheres for superior performance.