Effects of the Water/Cement Ratio on the Properties of 3-3 Type Cement-Based Piezoelectric Composites.

In this work, 3-3 type porous lead zirconate titanate (PZT) ceramics were fabricated by incorporating particle-stabilized foams using the gel-casting method. Then, Portland cement pastes with different water/cement ratios (w/c) were cast into the porous ceramics to produce cement-based piezoelectric (PZT-PC) composites. The effects of w/c on phase structure, microscopic morphology, and electrical properties were studied. The results showed that the amount of hydrated cement products and the density of the PZT-PC composites increased with the increase of w/c from 0.3 to 0.9 and then decreased till w/c achieved a value of 1.1. Correspondingly, the values of both εr and d33 increased with the density of the PZT-PC composites, resulting in less defects and greater poling efficiency. When w/c was maintained at 0.9, the 3-3 type cement-based piezoelectric composites presented the greatest Kt value of 40.14% and the lowest Z value of 6.98 MRayls, becoming suitable for applications in civil engineering for structural health monitoring.

Modulation and effects of surface groups on photoluminescence and photocatalytic activity of carbon dots.

To demonstrate the effects of surface atoms on photoluminescence (PL) and photocatalytic activities of luminescent carbon dots (CDs), we design and tailor the surface groups of CDs with heteroatoms by a facile and effective approach. The coexistence of O and N radicals in CDs results in strong PL while CDs containing O and Cl radicals show high photocatalytic activity. This is attributed to the different degrees and directions of energy band bending from inner to surface induced by O, N, and Cl radicals at the surface of CDs. The coexistence of both upward and downward band bending that are caused by the O and Cl radicals, respectively, in CDs is similar to an internal electronic field that facilitates the separation of electron-hole pairs and carrier migration, leading to high photocatalytic activity. These results may also be used for designing and tailoring optical-electronic properties of carbon nanostructures.

Carbon-dot-loaded alginate gels as recoverable probes: fabrication and mechanism of fluorescent detection.

We prepare a solid and green film of carbon-dot-loaded alginate gels with a pore structure. Compared to carbon dot suspension, the film exhibits stronger blue light emission. The porous structure of the film enables ion diffusion and contact with the CDs incorporated in the gel network, and thus the photoluminescence (PL) behavior of the film can be influenced by ions. The PL of the film shows a sensitive and selective quenching effect to Cu(2+), and it can be repeatedly used as a fluorescent probe to recognize Cu(2+) with a detection limit of 5 ppm. A band bending mechanism is proposed to understand the effects of surface/interface states and metal ions on the PL behavior of carbon-dot-loaded alginate gels, and it has been supported by our further experimental results. This band bending mechanism provides a clear physical insight into ion detection by PL behavior.

One-step synthesis of graphitic nanoplatelets that are decorated with luminescent carbon nanoparticles as new optical-limiting materials.

Graphitic nanoplatelets (GNPs) and luminescent carbon nanoparticles (CNPs) are simultaneously synthesized by controlling the laser parameters and the size of the graphite flakes. Because luminescent CNPs are attached onto GNPs, a new carbon nanostructure is obtained. Compared with carbon black, GNPs, and luminescent CNPs alone, this nanostructure shows better optical-limiting (OL) effects. The OL mechanism of GNPs that are decorated with luminescent CNPs can mainly be attributed to nonlinear scattering. The role of luminescent CNPs is to promote the formation and growth of nonlinear scattering bubbles, thereby enhancing their optical-limiting effects.

Thermodynamics of face-centered-cubic silicon nucleation at the nanoscale from laser ablation.

The thermodynamic nucleation and the phase transition of the face-centered-cubic structure of Si (fcc-Si) on the nanoscale are performed by taking the effect of nanosize-induced additional pressure on the fcc-Si formation under the conditions generated by laser ablation in liquid into account. The thermodynamic analyses showed that the formation of fcc-Si nanocrystals with sizes of 2-6 nm would take place prior to that of large fcc-Si nanocrystals, and the phase transition probability from diamond-like structure Si (d-Si) to fcc-Si is rather high, up to 10(-3)-10(-2), under the conditions created by laser ablation of an Si target in water. These theoretical results suggest that laser ablation in liquid would be an effective industrial route to prepare ultrasmall fcc-Si nanocrystals.